There are a few stick PCs on Amazon for around $100, though the specs are pretty minimal. I saw one for $109.99 with a $15 off coupon, but it's got only an N400 CPU, 64GB storage and 4GB RAM. It would probably be fine for basic things, but it's not upgradeable.

There's another one with a J4125 CPU, 128GB storage and 8GB RAM. It's $159.98, but with a $30 off coupon, so ~$130. I have one just like it, though with 6GB RAM, and it works very well. It's not a speed demon, but it does the trick.

If it were me, I'd get the latter, even if you have to save for a little longer. For what you're looking to use it for, it might just fit the bill. Whatever you do, don't buy something used. You might be buying another user's problems.

There's also a limited time deal on this mini for $129.99. Again, it's a little higher than what's you're looking to spend, but it'd be well worth the extra. Though I'm not very familiar with the brand, for what it has it's a fantastic deal, and if it being bigger than a stick isn't a problem, it would be what I'd go with. The N5105 is a great CPU, and it's got an m.2 SATA drive, which means it's going to be a lot more responsive than those two stick PCs. 256GB storage and 8GB RAM, and the RAM is dual channel. It's also upgradeable. Of the three, this one is a no brainer.