I have no real experience with the recent HK receivers. However I find it hard to believe that a refurb on Ebay is best. The Denon or an Onkyo 507 would be better. I know I wouldn't be happy with the low wattage from the 254 although it is mentioned that the amps are legit in HK receiver. Here's a cut from cnet.
Don't get spooked that the watts-per-channel specs on these receivers seem low. While other manufacturers tend to inflate their power ratings, Harman Kardon sticks to real-world numbers--in other words, Harman Kardon's 30-watt receiver may sound just as loud as another company's "100-watt" receiver.
Overall, these receivers are a big improvement over the existing models, but they'll face an uphill battle versus the competition. Onkyo's TX-SR606 has most of the same features as the Harmon Kardon 254--plus it has four HDMI inputs--and it's currently selling online for about $440. Sony is also offering four HDMI inputs in the midrange level, and the STR-DG820 only costs $400.
I know you said sub $300 dollars but when you are obviously willing to use Ebay, as I do, all the above receivers start coming down to that level.