If you buy a used one from eBay, I would ask if there are any stuck pixels and where they are. I returned mine once because it had 5 right in the middle of the screen. They didn't affect gameplay, but it was slightly irritating.
$40 is what I paid for my 20th Anniversary Famicon-style Micro during Black Friday about 3 years ago. But, mine didn't come with extra faceplates so I bought a few Famicon ones from Nintendo. I use the Micro often as I have a backlog of GBA games. So yeah, I'd buy another for $40 if mine crapped out on me.