www.buyfordmotorsport.com has 3.55, 3.73, and 4.10 gears for $139. That's where I got my 4.10's
If you've got a V-8 fox body it's got a trac-lok rear-end. It's probably just worn out. You can pick up a trac-lok rebuild kit with new clutches for like $80 bucks.
Stock gears for a 5-speed are 2.73's with optional 3.08's. Auto's came with 3.08's and optional 3.27's