AC line regulators

So I've been on tour with my trio + tenor and we've been recording all the gigs using a Fostex D160 harddisk recorder. Have not run into any problems until last night. The club had such horrible power that the recorder was freaking out... not recognizing the drive, seeing the drive but not able to read it, etc.

Furman makes line regulators that take anything from 97vac to 141vac and outputs a constant 120v at about 10amps. But they are $600. How difficult would it be to make something like this? Any ideas on where to start?

AC voltage regulators, at least the ones I've seen, use a transformer or autotransformer with several taps and a control circuit that drives a bank of relays to select between the taps. This switching is lightning-fast and, I presume, happens during zero-crossings, so devices connected to the output do not see a "glitch" in the supply voltage. We have a big-assed rackmount regulator (not a Furman) of this type in our TV truck and it works beautifully. You can hear it clicking away as the supply voltage and loads vary, but there's never a glitch.

I don't think it would be cost-effective to DIY. You can use a variac, but that's only good for compensating for a fixed error in the supply voltage; it will not ride up and down automatically as does a proper regulator.

This is a variac controlled by a stepper motor. It is pretty quick, but a lot to carry around, but may be cheap since it is considered a boat anchor.
but they are very rugged. Gen Rad i believe.

I guess I'll just keep my eye out for a used Furman. We played at the same club tonight and I just bought a 100 foot extension cord and plugged into the same outlet that they have their office computer plugged into and that worked. Got some good stuff recorded tonight!