Is it possible to get a good/okay quality used laptop for around $100?
you can build up a nice x200 for that, an okay x201, or a beat-to-shit, half dead x220.
I recommend the x200 route so you can get a NO HDD one without issues and still have enough leftover to get a new OEM 9-cell + power adapter + small SSD if you stretch the budget a bit.
That route's exactly what I did. Posting from an x200 with 4gb ram, 60Gb SSD, new OEM 9-cell, OEM power adapter. My total was ~$115 all built up. Would have been closer to ~$130 if I went with a bigger, name brand SSD like those ~$50 128GB sandisks
The cheap power adapters work fine too but the cords aren't as long which is sort of annoying