I use a Fireball V90 running on MACH3. I design the circuits in Eagle, output the GCode using pcbgcode(.org). I don't think you can get there any cheaper than this solution. I don't use a Dremel - too much tooling play, and not enough power. I use a Bosch Colt trim router. This setup is VERY capable, after you learn the machine and understand how to adjust it and keep it running in good shape. It isn't the most robust machine, but can put some great work out.
You can get them here:
http://www.probotix.com/
I got the large box with 40V power supply and the yellow motors, but you can buy a cheaper system with smaller motors. It would run slower, but still be capable of PCB work.
I started with 60 degree tools, but am now using snub nosed 0.015" mills and the traces look fantastic.