The last US sized comic I printed was Mickey Moose. We printed 200 copies for $600. It was 48 page B&W interior and full color cover. We got some dodgy copies where the ink was peeling, but generally it was pretty good quality. I also printed comics in the thousands (Quay-Line), which ended up costing 80 cents per unit.
Anyways my theory is that the reason printing comics is expensive is the same reason Matt pointed out. It's just a foreign concept to most printers in Australia. They are either used to printing thousands of brochures, magazines and panthlets or just a handful of random portfolio crap. Anyways my understanding is you're not paying for the print, but for the set up, and comics especially US size is a totally foreign concept.
Which is why I gave up on it and figured out some other ways of making my last few comics look interesting. I printed my last comic as an A6 landscape thing, and I was really happy with it and saved a bunch money. I paid $100 for 100 copies. I used the printer at UTS. The Turkish man there was really helpful, but I wouldn't say the same for the younger guys. I also found that I would buy my own stock of paper for the cover. That made it look nicer. Anyway going A5 or A4 probably will save you cost too.
Anyways I'm working on a new comic myself, and I'll be printing around 200 copies. I might keep you guys posted on the cost here. I think it's going to be cheap though. I paid something like $2 (2000 won here) for a locally made comic and it really looked the business.