I'm on a pretty tight budget but a set of 04 sti springs and struts just popped up. He said it has about 20k miles and wants $400. A friend of mine has offered to give me his extra set of 04 wrx springs and struts with 110k miles for free. He said it doesn't leak any fluid but with the high miles he is not that confident in them.

 

Installation doesn't really bother me but I'm wondering if 20k on perhaps a sti that was driven hard may not be far from the condition of a 100k wrx. I'm just not sure what to do..

You can't beat free.

Free and they should bolt right up.  The STI you may have to modify the mounts on the rear struts.

The rear top hats will have to be swapped no matter which struts you use. The STi and the wrx have the same top hat bolt pattern. But the first gen legacy has a different stud pattern.