You can find used 10/22s at the pawn shop from $90-$150. I saw one just yesterday for $115. Alot of times you can even talk them down a little. There was a Malrin mod. 60 right next to it, but I didn't ask the price. Mossberge has a couple of 22s for $100, Rossi has a 22lr/20ga combo for $120. These prices came from Academy's website. Not real sure what you could find in a centerfire for $100.
I bought a .22 LR Savage (Stevens) semi-auto at Wal-Mart a couple of years ago for $105. If your wanting something with a little more power you might be able to get an sks for around $150 (military used). That depends on what state your in though, I got mine for $75, but that's cause a friend got in a money pinch.