Midi Keyboard/Cubebase setup

a used m-audio keystation (keys, a midi-volume slider) will probably be your cheapest bet for full-size keys. feel is kinda mushy but they work.

for sure a deal on craigslist for a 49 or 61 key version.

if you want assignable pads, knobs and more sliders they have those available too - for more money. check m-audio.com

korg makes a super-cheap controller called the nanokey2 - might not be what you're after but it's tiny and portable.

 

Can you play keyboard instruments? Pianos or synths? If so then you know what you want.

Some cheap keyborads have a USB jack and the MIDI-USB interface is built-in. This is good but only if the K/B uses a good internal interface that does not require drivers. "real MIDI" uses two round DIN jacks but requires a separate MIDI-USB cable (with interface built into the cable)

Bring your Mac to thew store and plug in the keyboard and it should "just work" in Garage Band with not software/driver install. It it does not buy another one.

About CuBase. Many times yu can get it free as bundled software with an Audio interface. If you need an interface get the one that has this software and save a little.