For an excellent condition 92fs, with two 15 round mags, I'd pay around $400 if I were in the market. Less for worse condition.
It's a good gun, but far from the best for what it does. It's a massive 9mm pistol with strong capacity. You can get 17 round mags.
For comparison, there are a lot of excellent pistols on the market that are better IMO for the same or less money. CZ75, CZP09/P07, Glock, Sig, CZ999 ($280), XD, SW MP, etc. and clones of many of these...
If you love the gun and must have it, I'd say for an excellent one, up to $500 would be fair.