How do I hook up 3 computers to a wireless router and have able to share printers and information?

What has $300 have to do with your question.

Your router will come with instructions on how to do this. You can also find tutorials for this at PracticallyNetworked.com (http://www.practicallynetworked.com). If you have any specific questions please feel free to ask.

What operating systems with they be running?