Air Exchangers are a bit of an investment, but very low running costs. You could take it with you when you leave.
You can also buy a bathroom vent fan for about $20 at home depot, and wire it to a humidistat.. When the humidity reaches a certain point, the bathroom vent will exhaust the air (could use it in a temp plywood window)..
Most importantly, use alot of air circulation, preferably large industrial fans. If the moisture can't settle, it has less chance of causing damage. Circulation + Exhaust might be your least expensive route.