13b turbo, or the 20b NA
i have a 1990 2nd gen.

i was wonder what that average cost to do an engine swap is, for both of those motors, and which one to chose and why?

 

Covered many times. All you have to do is search.

To answer your Q:

20B = very expensive
13BT = less expensive (minimum 2500-3000 to do it right and in many cases much more)

 

Short answer:

20B = $20,000+ to infinity

13BT = $2000 - infinity (depending on the level you want to take this)

See the FAQ for detailed answers. There is also a 20B subforum here which contains a nice FAQ as well.