The 5sfe engine correct? It's a pretty beastly engine, I know people who have one at 250,000 miles and it's actually pulling harder than it is at the day you got it. Sldr also thinks that the Turbo cost for older cars MUST be the same cost it is for the 7th gen celi- 4k or thereabouts (where you and I could get an engine swap to a 3sgte for that much money).
Plan on the Turbo costing you about 1.5k, if you do all the work yourself.
You're going to need to rebuild the internals mildly and totally redo the fuel system (add a Supra TT fuel pump and new injectors)
But keep it on low boost and baby it at first, then as you start rebuilding stuff, up the boost! It's not unusual to see these oldschool celica engines doing 18psi
So, what Lark and AZZKIKR said combined