which size tire would fit after 2.5'' lift?
A small one?

A SPOA will be cheaper than a straight spring lift. It provides around 4 1/2"s of lift and you can run up to about a 32" tire. I have had 32" TSL Swampers on mine since I did the SPOA, since then I have added some 1" greaseable shackels which gave me another 1/2" of lift. I have also added a SKY 1" body lift for the clearance of the motor and other goodies.
If you or some one you know can do the work, a redneck SPOA done decent should be fairly cheap.
On edit;
Do check out Sky's site, he has some decent stuff. One is a nice SPOA kit that you can build on and not have too toss any pieces. Check out his stage 2 spring over kit, cost's less than $400 and you get some nice stuff with it.