The $100 ($200) is an upfront lease fee which means you do not own the receiver and it must be returned if ever you leave DirecTV. Just to clarify the "purchase" is a upfront lease fee and does not mean you own it. What this also means is that you will not find any reputable sellers selling used ones as they are leased and are not owned by the subscriber.
With that said, you can pick up a new receiver at any DirecTV reseller. I have purchased from these guys before, just not receivers.
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www.solidsignal.com/cvie ··· eceiversIf this is your first time into an MPEG4 or HD you may want consider that a dish upgrade may be needed as well. If that's the case your best bet is call back DirecTV and tell ask them to match your local cable cable or Dish Networks offer and give you a better deal on the upgrade and dish swap.
EDIT: also, regardless of where you get the new receiver, DirecTV or another reseller, you will need to commit for 24 months once you activate it.