Just remember that most cheap generators and UPS's are not compatible with our pumps and powerheads. To ensure you don't damage equipment you're either building your own or looking for something that process a true sine wave.
I have a honda eco 2000. It was pricey, but it's portable, the power is very stable true sine wave, very good on gas usage (throttle the motor from almost off to full speed dependent on load), I can run it on my front porch in the middle of summer and not keep the neighbors awake, and it will last quite some time.