Recently, I stumbled upon 'KPS305D' bench power supply on evil-bay. It goes for about 50USD and is rated at 30V/5A.
There are various models from 303D to 605D. The most expensive one is rated 60V/5A and priced around 80$.
It doesn't have an output 'on/off' switch, but I guess that could be modded easily.
Has anyone used one of these? Does it have problems with overshoot/undershoot?