I think it depends on what you considering "complete". I would say a nice one (with decals intact, no roof discoloration) with all accessories, box and instructions goes for about $300-$350, give or take depending on shipping costs.
If you don't care as much about condition and the packaging materials, you could knock off maybe $50 or more depending on what the flaws were and how bad they are.
The playset has a TON of accessories, some extremely hard to find, so that really affects the cost. Most people end up buying a mostly complete set and spend a lot of time (and money) tracking down those rare bits. If you're a patient person, this might work for you.
Shipping costs are another thing you'll want to consider. Due to the size of the thing, some people aren't able to send it in one box. The further the seller, the more it's going to cost too, so you might save on shipping by finding a set that's close to you (or even better if you're able to pick up in person).
I've also got one for sale, in good condition, but not 100% complete.