I got this frame cheap not sure if I should buy each part for it or buy a used bike for 100 and swap the parts.
I have the frame, fork, both derailers, crank set and stem.

I found these.
1996 cannondale 200 se
2002 trek 4300

Can I put a8 speed cassette and shifters on this 9 speed rear derailer I have on already? Or if I go this route swap everything?

I would then upgrade as things break.