Here's a thought, check out the tables and comparisons at:
http://www.desktopcnc.com/cadcam.htm
I'll warn you - there is a heap of info available and you'll need to check the pricing at each site - eg, STLWORK, is listed at 250 USD and its on sale now for $75 - so,you'll have to still shop around some.
If you can find a good CAD program in the price range and then get an CAM program to create a machine path and convert to g-code, and a machine program to run the machine - you're there! MACH2 as amachine program comes in at $150 - there are some DOS based programs out there at nearly - free prices, so its still a bit of a research challenge.
Good luck - Jim