First off, welcome to bikeforums.
It's not really a matter of being difficult to do. Your question is too general and we need help narrowing things down. You could find a number of different Suntour components affordably to put something nice together.
Still there are so many factors:
-Indexed shifting or Friction
-How many speeds, what is your frame's rear spacing.
-downtube shifters? Stem Shifters?
-Freehub or cassette
and on and on and on!
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