I think the $5k they offered would be a minimum reseller price on this category killer domain.
If you have no plans to develop it I'd go for closer to the $10k range. I think an end user Harley seller might pay $25k. I'd put a lot higher numbers, but people really aren't paying much for the Keyword. .66 cents a click with Medium competition. This could be higher in the spring though.
5k is a fair offer, but with some marketing or getting it in the right auction I think you could do much better.