i was thinking of a german amazon review site and advertise it on facebook ?
i know a little bit html and so on... but i dont know SEO :I
Two (or three?) years ago I was in the same place as you are now.
1. Do proper keyword research. There are lots of guides (on internet, not just BHW) on how to do it. Use trial version of Long Tail Pro or Market Samurai (or both!).
2. 100? is nice amount of money. I advise you to use it for domain and hosting. Go for cheap hosting, but read reviews first.
3. The first site should be in your first language, in German, so you don't have to invest in English writers. I haven't done any German site, so I don't know how difficult would be to rank for any keywords, but my first sites were in Czech language (as this is my first language) and it made some money (keep in mind Czech market is a lot of smaller than German one).
4. Learn how to do simple SEO (again - lot of great guides both here and on IM blogs).
5. Monetize your site with AdSense or Amazon.de (or PR articles, or selling links, or....).
Profit
Don't outsource too much with this tight budget. Do the most stuff by yourself. You will be happy to have the experience from it
PS: Don't advertise on FB (or anywhere) - 100? will be gone and you won't even blink (or probably sell anything).