If your printer is located near your wireless router, you don't need to buy a wireless print server. A wired print server is good enough for all your networked computers to print wirelessly.
If your printer is located elsewhere from your wireless router, then you need a wireless print server for all your networked computers to print wirelessly. Another solution is to use powerline adapters through your power sockets with your wired print server which may be more expensive. It pays to compare prices before buying.
Also, not all print server is the same. If you have a multi-function printer which can do scanning and faxing, then you need a special print server which support these functions in order for all your networked computers to scan and fax.