Only my high beams are working and not my low beams.?

The other night they were not working, so I flipped the switch back and forth a few times and my low beams finally came on. Last night it happened again and after flipping the switch back and forth only the high beams came on. I would like to know what the possible problems may be and how much I could be looking at. I have an 87 Bronco 2. Thanks Luke