Nobody will give you an exact value of a domain. It's impossible. The value of a domain is mostly given by the need of the buyer. After that comes the value of the keywords contained in the domain name, page rank, oldeness, traffic, rank in the search engines, if listed or not in DMOZ, ect.
About the estibot evaluation, it can be taken only as a guidance or a starting point in your sale. Estibot has some algorithms to calculate the value of a domain, wich are explained in their site. But again, a buyer might not value a domain as estibot does. Hope you understand what i mean.
To your prosperity.
Drunken Duck