I would start by stating that you had not planned to sell and that you would be interested in hearing what he feels the name is worth.
Make him make the first offer and react to this. If it seems low to you, do not worry, AND DO NOT BLAME HIM. If I was asked to make an offer I would of course start very low as I would not want to pay more than I had to.
Work from here, but if his offer is lower than $150, I would perhaps counter with $500. However, I do not know the traffic or revenue and this is a new market so it could be worth more to you than this.