hi
u can get a st170 engine convertion done for about 3.5k from pumabuild. obviously if you can do the work ur self u can cut the cost.
for anything higher, 1.8, 2.0l etc, everything needs to be replaced therefore it wont be the cheapest option.
i believe a puma 1.7 engine goes in well with a bit of work. but obvioulsy still only 1.7.

sure some more techy people will be along with it a bit more in depth, tho ill try and dig out some info i found when looking into my 1.6