Any advice on a sander that will do a decent job on the cabinet? I will most likely not use it again so I would ideally like something for under $100 - or am I dreaming? I can't justify an $800+one.

to strip decals or to strip residue and smooth the wood?

I now still use a heat gun and scrapper to get old stuff off and then the sander below (less than $100 new) with 'paint stripping' sandpaper first to get glue residue and then 80 grit and then 240 (or something like that) grit paper..

http://www.bunnings.com.au/bosch-270w-random-orbital-sander_p6200277

The dust catcher is a bad joke though, I do it in driveway (outside) as it makes a horrible mess ;-)