Getting profitable on just $100 isn't so likely, I'm afraid. But depending on your price point, you can get some usable data (maybe some sales) is doable.
A few steps to get you going:
1.) Set up tracking for Add To Carts and Sales. Sales are all that matter but ATC will let you track a faster feedback loop.
2.) Start with Shopping, if possible.
3.) You don't know your bestsellers yet, so research your competitors. Find out what their bestsellers are, and start by promoting those.If your competitors use Shopify, here's an article about finding their bestsellers:
4.) If Shopping isn't an option, consider looking at Bing Search. Cheaper than AdWords and converts pretty well. Smaller volume though. Once you have your campaigns figured out you can scale over to AdWords.
Hope that helps, and happy hunting.