Go join the canadian airgun forum if you want to consider using any kind of co2 gun to hunt.
1. You wont find squat in airsoft for $100
2. You plan on killing things with a plastic ball with airsoft guns? Dont think so..
If you were serious about getting an airgun for some minor hunting then you'd either know more about what you're getting into or make the effort to read up on it before posting on a site that doesn't have anything to do with what you're looking for.
Aside from that, pellet guns arent the greatest things in the world for hunting. ESPECIALLY if you only want to spend $100. Sounds to me like you want to plink and kill random tree rats in your backyard, thats not hunting nor is it good to try and kill things with under powered guns.
You need to do a lot of research and understand the rules and regulations for what you want to do before jumping in.