Here's how to make a custom keyboard for under £150/$150 | Eurogamer.net
Building a Custom Keyboard
Amazon.com: Casio SA-76 44-Key Mini Personal Keyboard : Musical Instruments
CT-S200BK | CASIO
RenFox Digital Piano Electronic Piano Professional Keyboard Piano 61 Keys Portable Keyboard with Music Stand, 200 Tones, 200 Rhythms, 60 Demos (Black) : Amazon.de: Musical Instruments & DJ