Please don't! Why do that when hosts like Pacework are offering affordable hosting packages as low as $4.99 per month? You better buy hosting.

Just buy a basic shared hosting package. It will be cheaper in the long run, than hosting yourself.

Well, you will not be saving anything by using a Mac as a server. It will cost you more in electricity and bandwidth. Plus, it is not designed to act as a server, unless for small projects where you use it as a local host.