High humidity in house when weather is not hot. Ok?

If all you want to do is bring down the humidity then rather then running your central a/c (which costs an arm and a leg) you can pick up 2 fairly inexpensive dehumidifiers for less then $50 in total at any Target or Walmart. I'd be more interested in finding out the source of the humidity. If its an old house, could there be a busted/rusted drain pipe leaking under the house somewhere? Hope that helps.