Buy a printer that has Ethernet (and/or wireless depending on which you want) capability built in, attach the printer, assign it a static IP address outside the DHCP server assignable range but within the network range in your router. Then from each computer install a network printer, either using the IP address or the add printer wizard. The computers should have network discovery turned on, which they probably already have turned on.
You can also just add a second printer to one of the machines and share it with the network if you can leave that machine on at all times that the printer is needed. Once the printer is installed, it can be installed as a shared network printer by the other machines if file and printer sharing is turned on. This might be a little cheaper since it has no network adapter built in, but is often less convenient.