It depends on your world. If you play in a world with drastic imbalances and/or one that supports tanking, you could have several people with 30M+ in prospect budget every year and IFA signings can be really out of whack. In general, I tend to have a lot of money into IFA because I zero-out advanced and budget low in high school/college scouting. Know your league and the other owners, In Happy Jack, there are 8 people who have transferred budget to have more than 20M in prospects, and two (including myself) with over 30M in payroll. Obviously, this is going to inflate salaries for many IFAs, especially toward the end of the season when people who have missed out on the big guys need to do something with that money before it goes to waste. In No Quitters (which I would consider to be a higher-level, more competitive league as a whole than HJ), I am the only one so far who has transferred to have over 20M, so obviously the bonuses will be a little lower.
But, in my experience, here is a general guideline:
Pitchers: Aces starters (200+ innings, 80+ control, splits, etc.) are very rare and will almost certainly go for 20+M. Essentially, if one of these guys pops up, most will bid their entire budget and then it just comes down to how much money the 2nd-highest bidder has in prospects. Even guys who are starter/reliever "tweeners" who might only pitch 150 innings or so in a season will still command close to 20M, but usually fall in the 14-18M range, which is also where starters who aren't quite ace material tend to fall. Ace relievers will tend to go anywhere from 8-18M, depending on how many innings they will be able to throw. 4th or 5th-starter types tend to cost around 10-12M. 8-10M for a starter and 6-8M for a reliever seems to be the lowest that sure-fire major league players will go. You can definitely still get guys cheaper who can make the ML, it's just either luck (because everybody ran out of money or didn't see a particular guy), or you are picking guys with obvious flaws who need to hit all of their projections perfectly to make an impact, or guys with really low health, etc.
A brief summary of some of the pitchers I've signed over the past few years:
No Quitters:
S10: 3.1M reliever with 70/20 DUR/STA and great control but who's vR never got over 50 and topped out at AAA
S11: 5.2M for a 30/60 DUR/STA tweener who will be in the majors next year, but only as a Long B guy. He'll be in the majors until his second arbitration contract demand, at which point I'll release him.
S12: 600k for a 70/12 DUR/STA reliever who would be a pretty good LOOGY, but that role doesn't seem to work in HBD, so he's probably going to top out at AAA, with a vR of only 51. For only 600k, a risk worth taking.
S13: 8M for a 4th/5th-starter type who I traded. Control might not break 60, but with solid splits, he'll definitely make the majors and do okay.
S14: 700k for a reliever kind of like the guy I signed in S12 who probably won't make the majors either. 2.5M for a starter with really crappy control, but nice other ratings who may actually make the ML if his control keeps developing another few points. 8.4M for a real nice 30/50 DUR/STA type who should be a very effective reliever.
S15: 7.8M for a solid, but not spectacular, setup guy. 3.4M for a starter who's vR will probably never get high enough to get him more than an injury call-up to the majors. 1.6M to a reliever who might be a borderline ML player, but I'll probably find better options in FA and never promote him past AAA.
S16: 16.4M for a 30/65 tweener-starter who is ML-ready and has ace potential if he hits his projections, which he probably won't since he's already 22.
Happy Jack
S14: 800k for a reliever who will almost certainly make the majors. Not a star by any means, but I was shocked to get a sure-fire ML player for so cheap.
S15: 10.8M for a starter who seems unlikely to be more than a mop-up guy. 8.4M for a 5th-starter with nice DUR/STA. Won't be great in the ML, but will be at least signed through his first arb demand. 2.5M for a long reliever with nice splits but crappy control who probably won't make the ML.
S16: 11.6M for a solid 2nd/3rd starter. I was shocked he went so cheap, but he popped up early in the year and I think people were waiting for the bigger fish. Signing him cost me the chance at a 20M+ guy, but I felt that the value was too good to pass up. It may have been a mistake as a significantly better player was signed for 24M that I might have been able to sign. Time will tell.
1B/DH/LF/RF- These seem to fall into two groups: the guys who will almost surely OPS .850+ as a major-leaguer will go for at least 15M. The guys that will be decent, but not spectacular bats, seem to go for 5M or less. I don't see a whole lot of these guys signed in the 6-14M range, unless they have a low health or DUR rating that scares some owners away.I got an above-average fielding RF with 57/82/83/71/91 hitting ratings (so he should OPS close to .850 in the majors) for 12M, but he only has 76 DUR and 67 Health.
Catchers tend to be a more exaggerated versions of this. The elite guys will command a huge price but all the others will tend to be pretty cheap. For guys who can mash though, be prepared to shell out some cash. I signed a C for 18M who is an absolute monster against righties, but not super-strong against lefties and whose DUR is topped out at about 67. Expensive for a platoon player, but possibly worth it considering the scarcity of good defensive catchers who can hit.
SS/CF- Want a guy who can really hit? 20M+. Want a guy with a decent major-league bat? 10-15M. Even an average fielding shortstop with a below-average bat will command 5M+. I did manage to find a 83/84 range/glove CF who's not a total disaster at the plate for 1.5M, and he's on my ML team in No Quitters, but he's purely a 24/25th man on the bench. I've signed 4 of these guys in the 1-3M range and two of them won't make the majors and this guy, along with another, look to be bench players/defensive replacements.
I signed a SS with a great glove but so-so bat for 9M, and another with an excellent glove and okay bat, but who's also a pure platoon player (with 16 vL, 93 vR, one of the craziest platoon splits I've ever seen) for 1.5M. I traded both though.
2B/3B- Hard to tell, because people put different values on defense at these positions. For the most part, probably comparable to how the SS/CF's go, I signed a 3B for 9.5M who turned out to be ML quality, but nothing spectacular and won't be resigned after his 2nd arb demand.
There's kind of two different IFA strategies:
(1) The "one impact guy" strategy. Either wait until after draft signing or estimate beforehand how much you will need to sign your picks, and then be prepared to spend everything else in your budget on one guy. The risk here is either going in too early and missing out on a better guy later, or else waiting too long for a top guy who never appears (or waiting for that top guy and then getting outbid by somebody else with more room) and then overpaying for middling guys at the end of the season. Can also be risky because even with 16-20M in International Scouting, you won't see everybody. I also tend to think it's more worthwhile to grab an IFA early in the year so they have that full season to develop rather than late in the year where they are basically wasting a year of development though. That may be wild speculation though.
(2) The "value" strategy. Bid on every (or most) quality IFA until you get to the point where it's not 'worth it" any more. A great way to stock your farm system with solid major league players as you can often grab 2 ML-quality players every year with this method. Unfortunately, you will probably never get an All-Star caliber player this way as you will likely not have enough in your budget when that mega-star is found. I tend to lean toward this method, and just be prepared to go all-in for a top quality player if they show early in the season.
I hope that helped.