If you're just needing something to see bullet holes in white paper at 100 yards, you can get one for under $100. Bushnell makes a 20-60x60 which sells for about $90. You'll probably find yourself using the 20-30x range more than anything else. beyond that, lower end spotting scopes lose a lot of image quality and focusing becomes bothersome.
Check pawn shops and such- might be able to find a good deal.
Nate