If you're looking for an affordable MIDI controller to make beats on and you'd like to do a little DIY in the process then the Rhythmo BeatBox could be exactly what you're looking for.
The Rhythmo is an all-in-one DIY MIDI controller drum machine kit and mobile studio that will eventually have an associated App for making beats.
You can find them on Kickstarter right now.
Compact and class compliant audio
From military deployment to the MicroKorg
Plans, future, lockdown
Freeze for the hot weather