Yamaha's more affordable Tenori-on Orange may be arriving just in time for Christmas, but it's still not exactly cheap. If you're looking for a grid-based synth that does fall within a realistic budget, though, you should consider ThinkGeek's Bliptronic 5000.
Billed as an LED synthesizer, it certainly owes a debt of design gratitude to the Tenori-on, being based on an 8x8 matrix of light up buttons. Music is made in a pattern-based fashion, and the built-in sounds are of a retro nature.
Control dials enable you to pick your instrument type, adjust the tempo (the range is 60-160bpm), set the volume and turn looping on or off. There's a built-in speaker (plus line-out and headphones sockets) and multiple Bliptronics can be linked together. The fly in the ointment is the lack of a MIDI Out.
The good news, though, is that the Bliptronic 5000 is available now for just $49.99. Check out the video below for a demo.