I bought a used deLonghi dehumidifier on Trademe for about $100-$125. Some here expressed concern about buying a used one (used mold!) but it was clean and hardly used - plus I washed it well before using it.
My house is insulated so I don't have a problem with mold but I have asthma so when I feel wheezy, I run the dehumidifier for a day or two. Earlier in the winter, the indoor humidity was up around 60% so I'd run it until the humidity level dropped to around 50%. Now the indoor humidity stays around 48%. I only turn the dehumidifier on when I notice the level rising a bit. I'm guessing that having it on for days at a time has dried out the house and furnishings. According to consumer.org, it costs about $1 - $2 to have it on for 24 hours.
I was gone from mid-May through mid-July. I kept the house closed up but my neighbour turned the dehumidifier on a few days each week. After two months, I came home to a very dry and clean house. I didn't even have to dust!