It's well worth the money. Don't think of it as a computer game think of it like a virtual lego set since that's basically what it is. If anything else I'd say it's probably the best computer game for kids to play together as it encourages not only teamwork in survival mode but also true creativity when you play in creative mode with unlimited resources.
As for for hosting a server a buddy of mine hosts our minecraft server and uses FreeDNS to make it so that his IP always redirects to the server. His server is a dual opteron machine I believe which was built cheaply since all it hosts is minecraft and a web page. Best advice is pick up a cheap used workstation from one of those places that deals in off lease business machines. Run that as a server and you're golden.