Receiver Upgrade Advice

I recently bought a second HD television and want to upgrade my receiver. Since my main receiver is an HR21-100, DVR is not essential, but would like to have it if the price is right.

I am also a newbie to DirecTV, having only been a subscriber for a few months. and wanted some experienced advice as to the best place to go to get an HD receiver.

I know I can get the latest basic HD box for $100 at Best Buy/Circuit City, but am always looking to get the best deal.

At the end of the day, are there any discount retailers that sell either new or used boxes, and what are the issues with buying a used box? I have seen some chatter about older boxes not being able to pick up all the HD channels and am also wary of buying something that won't work and getting left out in the dark. Also when buying a used box, is there some problem with the whole "every box is actually a DirecTV lease" issue?

I am just looking for some direction about whether it is worth it to shop around or if I should just head to a local Best Buy and pay retail.

Thanks in advance,

Patrick