How about a drum machine instead of s/w? You could probably get one used on the cheap. I saw this ad a few seconds after first reading your post. This is from a local board but you could probably find the same kind of thing.

http://halifax.kijiji.ca/c-buy-and-sell-musical-instruments-pro-audio-recording-equip-Yamaha-RX11-drum-machine-W0QQAdIdZ224683561