Disc sanders are easy / cheap to make. I built one with an old 1/2 hp motor, any pulley that will fit the shaft (this will be the flange connecting the disc to the motor shaft), a scrap of birch plywood, and a couple of bits from the scrap wood box.
1) Mount the pulley on the shaft,
2) turn the motor on and dress the face of the pulley with file or bit of carbide,
3) drill & tap 3 or 4 holes in the pulley and mount the birch plywood (cut to a disc) to the dressed face of the pulley using counter sunk machine screws,
4) turn the motor back on and dress the plywood disc into a perfect circle,
5) build a quick base and sanding table with the scraps, (mine's just a flat piece of plywood to mount the motor on with a square block of wood on it at one end that acts as the sanding table)
6) mount the motor to the base,
7) apply the sand paper,
8) make dust.
With a scrap of sheet metal (i used a #10 can) and a hose mount, it's easy to rig up dust collection as well.
All in, it cost me about $25 (assuming $15 for the used motor and $10 worth of other bits), and a short afternoon.
It's not a beauty contestant, but it works perfectly - has for years.