A '91 should be a roller cam engine. New rings, new cam, rod, and main bearings, gaskets, timing set, new oil pump, and fluids/supplies should be less than $300. However, you will likely have some machine shop costs, including regrinding the crank, hot tanking and crack checking, possibly boring (requiring new pistons), and likely some head/valve work. I can easily see the total getting closer to $1,000 if you do all the disassembly and assembly work yourself. That's pretty cheap for a fresh engine. Then again, you can get a reman crate engine for about the same price, or a new Goodwrench/Targetmaster engine with a warranty for $1,800 or less:
http://www.sdpc2000.com/catalog/123/...R-U-L0557K.htm
http://www.paceparts.com/index.asp?P...D&ProdID=42989