Just search 40w laser engraver on ebay and you should get several hits around $400. Mine is working great after some mods.
Mods:
~$25 for 8ft ground rod and wire
~ $35 for 24V DC power supply( includes 5 volt supply because I blow out the DC section of the board it come with)
~ $45 Raspberry Pi CNC Board + drivers
~ $35 Raspberry PI
I can scp dxf files to the raspberry then rdp or ssh -X to open bCNC. Open the file and click Run. bCNC just added laser support so the setup is trivial.
I'm not too sure on the cutting power though. I have done paper, leather and cardboard but the 1/8in plywood I have tried is too thick.
I also had to put a 3904 transistor and a resistor in the board to make the laser on signal be sinking.
