Hitachi Ultrastar HUA721050KLA330 500GB 7200RPM 3.5" SATA HARD DRIVE | eBay
Set X 2 Microfonos Karaoke Con Cable Ps2 Ps3 Pc Xbox 360 Wii | MercadoLibre
An Ultrastar port should be interesting for add in retropie, with usb mic support in order you can do a portable karaoke for eady play in any TV or bars, pubs, etc :
Micrófonos SingStar de segunda mano por 10 EUR en Zamora en WALLAPOP
UltraStar: Setting up the Microphones | The Bricky Blog