That sounds like me, my last two grows. I was running one 600w bulb, one 8 bulb T5 panel (54w HO, so like 432w) two inline booster fans, and a centrifugal fan, and two water pumps, and like 6 air pumps, all off of one outlet, which I ran through an extension cord from my room, into my closet.
At one point the temps were really high so I bought an 8,000 BTU portable AC unit and ran that for like two weeks (which made the lights dim, but did not trip any breakers) until I got the electric bill.. then I unplugged that thing. Still.. thats gotta be like 2,000+ watts on one outlet.. in a shitty apartment.
Now I live in a house, and have got 4 600's vented, hanging, and bulbed up ready to go... but have the same question concerning extension cords. I cant burn down this house, thatd be no bueno, but I dont want to spend the little cash I have on getting an electrician to come wire a subpanel in that room.. especially if I can just run some extensions from other outlets on other breakers.. plus I would have to take EVERYTHING down, and then reassemble it, and Ive already got my seedlings sprouted and ready to go in their systems.