What the price of server computer?

You'd need to be a lot more specific. Are we talking a simple file/print server for your home network here, or do you plan on running a web service for 100,000 clients on it?

At the low end, you can reuse an old computer for a server (cost: effectively free). A high end multiprocessor server with terabytes of storage could cost tens of thousands (and if what you're doing is important enough to spend that much, you'll probably want at least three of them... one for development/testing, and the rest for load splitting/failover).