I'd stay away from the iBook unless you know what you're doing. I grabbed a higher spec 2005 model (1.33/1GB/80GB) off eBay for $40 too. I wouldn't pay more.
I too would suggest a Chromebook or the Stream 11. I'm not too fond of Win 8, but at least it's a full OS if you need it. But the Chromebook should be less prone to bloat and malware.
You can usually find used laptops around $100 on Craigslist/eBay. I sold my old Dell Vostro for $80 last year. Worked perfectly fine. Had Windows 7, Office 2010, dual core AMD Athlon X2, 2GB RAM, and a 160GB spinner. A decent browsing/writing machine. Slow, but it got the job done. Much faster than an iBook though.
I'm not questioning your info but where are they for that price? The lowest I found was $300
Saw a couple on eBay for $110-115, but without an OS or without an HDD. So, no functional ones.
I grabbed a perfectly good 2009 MacBook for $199 middle of last year. Deals can be had there, just have to be careful and buy from a good seller.
But for $100, a used Chromebook sounds like the best option at this point. DON'T get a netbook though. Run away from anything with an Atom, and Win 7 starter.