I'm looking to build a cheap server that can host anywhere between 10-20 (or more?) people streaming from an encoder with rtmp. This server doesn't really need to use server specific parts, just whatever works. This will be the only use for the server at the moment, but I would like to be able to upgrade some components later on. My budget is about $500-$650, the cheaper the better.
P.S. This server will be running 24/7 for the most part, so good air-flow is a must. At the same time I would like a smaller form factor, but I can sacrifice that if need be.