I do a lot of international travel and I just google "bag laundry service" wherever I'm staying. I can always find local laundromats who'll do laundry "by the bag" and will pickup/deliver for a much lower fee than what the hotel charges.

Interestingly enough, a lot of hotels send their laundry to these same places - if you're willing to make a minimal effort and contact them yourself, you'll save a TON of money.

Shameless plug for Sydney, AU travelers in the CBD: Wash On The Rocks!

Travis