WiFi-enable USB printers with a Raspberry Pi and share it over your network
Hands-on: adding AirPrint to your home network with xPrintServer | Ars Technica
Amazon.com: Epson EcoTank ET-28 Series Wireless Color All-in-One Cartridge-Free Supertank Inkjet Printer with Scan and Copy, Bluetooth, WiFi, AirPrint, Photo Printing, Bundle with USB Cable (Black) : Office Products
Brother RJ4040-K | RuggedJet 4 Kit 4" DT Printer with USB