What should I budget for 4.10s

Gears $200
install $200 -250
install kit $100 (if needed)
chip $300 (may need chip due to shifting problems like hitting rev limiter, I did and have read many others had this problem with 4:10's)

Best case $400 (cheap labor and no bearing needed)
worst case $850 (high labor, bearings needed and custom chip to correct shifting)
 
Just depends on what you want to replace. Are you going to rebuild the t-lock?

If you just want to do the minimum, then I would get the FRPP gears from ebay (got mine brand new for $140), then buy a differential shaft locking bolt ($5 @ NAPA) & some friction modifier ($8 @ FORD).

If any of the bearings are bad, then they can get autozone to drive the parts over to them. They are cheap.

That is all I can think of. My brother paid $250 for the installation on his 03 GT.

But if I was you, I would spray the ABS sensors with penetrating oil the night before, because shops don't usually do that, and when they break the ABS sensors & you get charged for it.

When I did my gears, the ABS sensors came out like butter. I know the penetrating oil help a lot!
Scott