I think mid xxx to reseller, enduser, its really going to depend on their budget, but anyone who is looking to start a online payment processing company, I think, will pay a nice chunk for it, low x,xxx...
Although I have to say, LivePay.com would be a much better domain.
I think if you have a small investment in the name and they are offering a decent price, jump on it. Just make sure that they are legitimate buyers and to use some type of escrow service.
Good luck!