Unfortunately, running a dehumidifier eats electricity, especially in the summer, since it's basically an air-conditioner/heater combo.
If you have bare concrete or cinderblock walls, waterproofing paint is a better option. We had it applied to our basement walls before we moved into our current house ~7 years ago and it's been great. We still have a dehumidifier from our old house, but we haven't needed to use it in our basement anymore.
We used Drylok wall paint: http://www.drylok.com/