1998 Chevy Malibu Fuel Level Sending Unit

My gas gage isn't working. I was told it that it is probably the Fuel Level Sending Unit. Can you tell me about how much this cost to have repaired. Also if I don't have it repaired can it damage anything else. I can allways fill it up at say every 200 or so miles. Also will my car pass inspection if the gas gage doesn't work. I was told that the cost to replace the sender unit is $600.00 +. I really hate to put that much money into an 11 year old car and don't have the money anyway but I sure can't afford another car right now.