I know where you can get FRPP 3.55's or 3.73's for cheap, but the 4.10's are about $160 and I don't think that's much of a deal. I went 3.73 for S/C. So if you decided to go that route let me know. Somebody will chime in with some 4.10 prices.
the frpp 4.10s are not in stock at MustangTuning and won't be for a few weeks. I had to buy mine from www.gefracing.com and they were great to deal with. I also recommend www.buyfordracing.com and $160 is cheap for FRPP 4.10 gears