Given the season, and with the plastics, I think that's a fair price. I'd do it. When buying private sale, I like to be fair to the seller too. I've been on the other end of that scenario a few times selling a bike, and it was almost offensive some of the lowball offers people threw at me on my already low asking prices. Price haggling in my opinion should be a compromise between two reasonable points and not an unconditional surrender for either the buyer or the seller. A dealership however is different. I'll go as low as I can, bluff, whatever. They are in a much better position to just say no if they don't like the offer and wait for the next and not waste their time playing the game.
Just my little "golden rule" philosophy on buying and selling...