It's not worth anything to anyone except yourself. An eBay account is not a marketable commodity like a domain name. The only way you can realise its value is if you are selling your entire business, and the account is one of your assets. But, even then, you would need eBay's permission, and I suspect they would not transfer the feedback score to the new owner.
What it's worth to you is another matter. But you're the only person who can decide that.
Shake