Dual Action Sander, bang for the buck

Hutchins is a finish sander with a tight pattern. A National Detroit is good for material removal. 80 grit is the coarsest paper you should use.
Dynabrade is another good brand. Ingersoll Rand is good as well. The CP would probably be ok for the price. The cheapies usually don't last long and are air hogs. 6" is what you need. Sandpaper is easy to come by for those.