Knives man I've gone through some - some are just hopeless
Unfortunately - outside of your price ..... Dexter ($60-70) consistently good , sharpen well - commonly used by pro fisherman .... worth the coin though
Avoid Swibos ....
But to answer your question
The best value filleting knife (IMHO) is the Victorinox 47513 ..... you should be able to get in on ebay for $40
6" & it holds a good edge
Chris