there were a southamerican company (chile maybe) wich makes more interesting little synth than this (depending on what you're searching).
for what that musician in the second video makes a kaoss pad could do the trick, for example.

a monotribe would be a good alternative to one of these (still not as cool). you can get alot of weird bleeps and bloops out of it

weird sound generator?

http://musicfromouterspace.com/index.ph ... 24&VPH=500

There's a ton of lo-end little synths like this. First one that springs to mind (aside from those already posted) is the Thingamagoop.

http://www.youtube.com/watch?v=8_QFHI3lDiw

You ask me they're all pretty much dub sirens in new and nerdy packaging:
http://www.youtube.com/watch?v=ul8GKV7m8O4

Monotrons are ok, but I think you'd have more options w/ the others....I dunno I sold mine it got old quick, some ppl love them.

another cheap option: Atari punk console through a delay/synth pedal