Indeed - 13 years ago, I had a side-line buying junk PowerBooks on eBay for very little ($100-$200), cobbling them together into perfectly working machines, and then selling them on for $1000+. I only ever tied up ~$2000 at a time, and would sell working parts I had no use for on, and even broken parts, as someone will want it, even if not for much. Never did any deep repairs, just part swapping and replacement.

As an added bonus I always had a snazzy laptop, as I'd sometimes hang on to a high spec machine for a few months before selling it on.

From what I can see on eBay today, it's still an eminently viable cottage industry.