How deep is your well? how big is the casing? How much draw down? What kind of pump are you using?

If you're using a submersible, things get complicated in a hurry. Jet pumps; however, are a breeze to set up so they don't pump the well dry. If you're using one of those, I'll tell you how I dealt with your situation.

As for the level monitor, I have a sump pump controller that could be adapted to turn on a light when the level got high and turn it off when it reached the lower limit. The thing is two insulated, low voltage electrodes. You set one at the low level and one at the high level. When the water in the sump touches the top electrode, it turns on the pump. When the bottom electrode no longer touches the water, the sump pump shuts off. No reason you couldn't hook up a light bulb instead of a sump pump. I'd check the hardware store, in the sump pump section. You would need to add wire to the electrodes, but that shouldn't be a big deal.