Honestly, it can't be done. Used is your only option. Pawn shops, eBay, etc. As mentioned above, there are a few choices in the $250 on up range. If $100.00 IS all you can spend . . . go with iron sights. And get close! (lol)
I'll presume you are new to this so let me explain features you would want should you win the lottery. A variable powered scope (3 - 9X for example) is a scope that can be adjuted from 3 power up to 9 power. 3 power would be prefferred in heavy timber where you can't see far and want a lot of your subject to be in the view of the scope. On up to 9 power where you would want to shoot at farther distances (200+ yards). And everything in between. Optics are very important to shooting. Cheap optics can be easily thrown off by not only bumping or dropping the gun, but I've seen them shoot craps just from the recoil of the rifle! What good is your scope when you have that 32 X 40 buck in your brosshairs and only to miss the shot!?
Durability, clearness of view in low light situations, and one that fits your rifle are the three features you need to have. Don't think you can do it for $100.00. Let us know what you come up with.