Seems every time my fielding instructor doesn't resign, It's time for the worst part of the game, trying to sign a new one. Owners pay 2 and 3 million for one which I'm not willing to do and the bidding wars for good fielding instructors are the worst. Is it that important to have a 90's rated guy instead of an 80's rated guy?

I'm interested in opinions on this too.  I always bite the bullet and spend 3 to even 5 million on the best available since they usually resign for 750k.  I take the one year hit to have one of the best for usually ends up an extended period.

Fielding instructor is by far the most valuable coach in HBD, as he affects all position players at all levels. You should always strive to get the best one that you can.

First thing I do after rollover is see which coaches want to come back, first one I check is the FI. If he's leaving I know I have to bump up the coaching budget by 2 or 3 mil.

At least in the world I'm in, there's usually a scarcity of good FIs, so you have to pay up or risk not having a big league level FI. Unlike, say, the backlogged 40 or so big league bench coaches who go unsigned.

In my three quality worlds, we have 5,5,3 FI making more than 3m.

As for your question, the difference between 80 and 90 probably won't be noticeable.    The difference between 40 and 70 will.

Mike, what is the lowest rating you would sign as a fielding instructor?

Ideally, I want 70+.   I've gotten stuck with mid-50s and I've noticed a point or two less development than I would have expected.  I've not noticed a difference in "normal" development in the mid-60s.

I don't have a problem with a 70's guy, in fact  I took a 70 guy over some higher rated because he had a 70 loyalty rating, even tho' I'm not sure how much that matters. The problem I have is that in my worlds, a 70's FI are rare, your choice is to get in the bidding war or end up with a 40-50 type, which happens when I lose the war.

if the bidding on the top 1-5 guys is crazy, can always be worth it to check the list of available ML bench coaches and minor league coaches to see if there's anybody hiding in there with 80+, you can offer them ML FI too

There are bidding wars for FI because the resigning bug makes them move valuable (in $ terms, not just skills) than other coaches. Assuming the coach will resign twice, if you spend $4M for an 80 FI now, you've got 3 seasons of a top FI for $5.5M. If you spend $4M on a top HC/PC who will resign twice, you get 3 seasons for $12.5M. If you don't want to spend what your world has determined top FI are worth, as pj noted search other MiL coaching roles and make offers to the best options you see there‚ not necessarily 80s; anything better than what you'd end up with from the FI pool leftovers. When my FI won't resign, I immediately bump up my coaching budget by at least $2M. Sign one who is near the top, and chances are you can save a few million the next few seasons.

I will spend $5M on a top notch fielding coaching without blinking.  The difference between those two 80+ rating FI and the other ones remaining to hire in the 50's/60's is too great.

That said, the difference between 70 and 80 is more negligible.  I just don't want anyone lower than 70 in most cases.

I don't know about fielding but I know that a bad ML batting coach can have a tremedous effect on young ML players.  I saw sopmeone with a hitting rating of about 10 and the younger players went down between 5 anf 10 points in contact, eye and splits.