I'd say if you find an individual/company who is going to make a new control panel, you could probably get between 75-150. But if you were smart you would give it to them for free and ask for a percentage of each control panel license sold during the first 6 months.
It's hard to place a value, if someone wants it badly, they will pay well to buy it. It would be good to do some searching and some sales approach on your own to find propective buyers, don't depend on auction sites where they would evaluate it and set a high price on their site but no takers.
From experience, about 2 years ago I sold a domain name for $5,000.00 to a corporate firm where I had the .com and they had the .net with the same name.