You could get a couple deep cell marine batteries with constant topping off performed by a battery tender and then plug it all into a power converter.
1x Large Marine deep cell battery $90-$120
12V Battery Tender $50
Power converter $35
I would say the above set up would keep your tank vitals going for a respectable amount of time.
I myself have been looking at a generator. Home depot has a Ridgid 3,600w generator with a Subaru motor for $499. According to my Apex, my tank uses 770watts or 7 amps of power when it is full throttle. It should be enough to keep my tank going, fridge, sump pump and furnace if needed.