You don't need a wireless printer necessarily as you can connect a network enabled printer into your router by using one of the ethernet cable ports. Depends on the physical location of printer and router as whether cable or wireless.
A good value network printer options is
Wireless network option is more expensive see for example click here
As you already state there is an option to use an existing or cheaper printer and buy a network print server box to put between your router and the printer. See example click here
Issue of Mac and Windows PC depends on availablity of drivers for the printer as you wsill need to install these on both computers.
Hope this helps.