This link is to the original project for a square wave midi synth, which I based my synth on, and has the info you would need to put the midi together, although the pins are different in my current  version. See the previous post below. You just need the midi input circuit on a breadboard, and a midi jack, I cut one off of an old PC midi adapter. The Launchpad itself is $4.30 from Texas Instruments.
 http://forum.43oh.com/topic/364-launchpad-simple-midi-synth/