Well my friend my best advice is do some quick research on sites like estibot or valuated, is the domain generating any revenue? if so ask for 5x what is making per year. If some one approach me tobuy a domain I will say yes, here is my counter offer, what you say, what you think? When you think is the next time you will get an offer to buy them? Did you have the domain for sale or want to keep them? Is like a house, you plan to die on it, or you want to sell it and buy others?