Since you have a lathe, you already have a disc sander. Dedicate a
faceplate (or make one with a block of wood, side grain, drilled and
tapped for your lathe), attach a piece of 3/4 ply, round it off at
desired size, apply a velcro pad, or finish the ply for self adhesive
discs. Build a box to sit on your lathe ways, clamped or bolted down,
with the end toward the disc open and a dust port in the other end. The
height of the box should match the center of your spindle. Voila! A
very cheap variable speed disc sander.
I'm of the opinion that I already own enough MOTORS, and have to fit my
shop into a single car garage space, so every time I need another power
tool, I try to adapt one I already have.
Now, if I can just figure out how to make a belt sander for my lathe, I
can get rid of that dinosaur powermatic I have around...