I've been thinking about buying a PVR for a while now because I'm fed up with my 3900. Should I get a 501 or a 721? I have a good idea of what a 501 is but I have little idea of 721's. How much does a 721 cost and what makes it better (or worse) than a 501? A new 501 costs $299 on the Dish site, but is there a place I could get a NEW one cheaper? Thanks in advance!