don't forget about hidden costs too. such as wiring harness conversion (if you don't do it yourself). i'm trying to remember, but the 91's came with power steering, right? if not, you need to aquire a power steering system from a newer 240 and put it in. if you do it yourself, you can save a ton of money on installation costs. i would estimate about 4000 for parts, then you'd have to add in labor costs. if you want a good rough sketch of what goes into working on this swap, go to
http://www.sportcompactcarweb.com. they outline an SR swap in the tech section