Look at the World News page for last seasons draft class. You can see that the lower that the player gets picked (lower in the draft, not lower number overall), the less money he gets. For instance, the first overall pick will sign for $4MM if he is a slot money guy, then each slot is about $90k less than the previous slot guy. However, you'll see picks where the money jumps up instead of jumps down despite the player being picked lower. In this instance, he was not a slot guy.
The language used by the scout for signability varies, but if he is a "probably won't sign" guy, he will ask for about $7.5MM so if you don't want to pay him that, you will want to move him down your board. The other non-slot guys will also initially ask for more than slot money, but it is usually like somewhere between 20-60 percent more than slot. Also, sometimes, a few days after the amateur draft is completed, the player may decide that he is interested in signing a baseball contract, but he ups his demands to even more that what he demanded and sometimes this can turn into a guy want between $5-9MM to sign.
If you don't have high picks, you can get away $5MM or $6MM in draft money and sign all of your picks if they are all slot guys. But if you have high picks or you have supplemental picks or you have guys high on your board that are non-slot guys, you want to have at least 10 million unless you do what many owners do by not signing any draft players past the round of 5.
I was in both the Intl market and the HS draft last season in Glavine, but since I spent $22MM on my draft picks, I didn't get any significant Intl players. I had comp picks and drafted two "probably won't sign guys". One of them signed for $7MM and the other signed for $7.5MM.