Sure, I believe you can send them either an E-mail or some correspondence directly from the domain/site you entered.
Offer what you feel it's worth, and mention that you'd like to negotiate ... and though I've never had occassion to do this, can't see the harm. If their posted price is "firm" / "Buy it Now" they'll likely let you know.
PS. Watch out for their pop-up's/under's on the domain/site. :cy: