On what? If you're talking about having pleasure then try buying one full round of beer at the pub nearest to your home. Else if it's for web marketing, I would use it for article marketing - get as much re-wrote articles as I can and submit it them to good article directories like EA and Amazines.
$100 is too little to do much. Either save it and continue what you did to get that $100 or buy articles as said above. If you're taking the article route, buy unique articles at say $3 a pop around a niche of a specific CB product or something. With 33 articles, use 3 of them to make a Squidoo lens, Blogger Blog and Wordpress free blog. These should point to a site you will create with say 15 of the articles (provided you have a domain and hosting). Send the rest of the articles through EA and other article directories. Have some of them point directly to your affiliate link and some to your minisite for presell and see which one converts better. After getting some sales, use the profit to rinse & repeat. The site should also do well in search engines too. You may want to monetize it will ads like Adsense and CPA offers. Later on, you can then flip the site for more profit Good luck!
There's no fix answer for the question - articles who get ranked on a high-demand keyword might offers tons of traffics; otherwise, you're likely to get 30 - 50 visits... per year! What R-ampage mentioned can give a rough idea on how the pros are doing. It's your money and to maximize the return on your money spent you must come with a systematic plan. What will you do with the articles? How are you going to submit (the sequences)? How do you maximize the usage of the articles? All these are questions to be answered before spending your $100. Personally, I would suggest rewriting all the articles again and again for article as well as Squidoo/HubPages submission. On the other hand, keyword research should be done before starting off your website or article marketing campaign. It's like the compass in your Internet marketing venture - it's the only way you can know that you're going in the right direction. Hence, consider spending a small portion of the money on this.
that's what we were selling u-bot for before we released the free beta. haha... guess I missed my chance