The DirecTV DVRs give you 2 tuners per DVR.
You can:
Record 1 show, and watch another
Record 2 shows, and watch one that you're recording
record 2 shows, and watch something you've previously recorded.
The DirecTV DVR fee is 5.99, and that covers all DVRs on the account.
The DirecTV DVRs you receive may require 2 coax lines going into them
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DirecTV is currently offering a promotion to give you 1 HD DVR for free if you sing up for the NFL Sunday Ticket.
Otherwise, there is a 1 time lease fee for DVR's at $99, and a 1 time lease fee for HD DVRs at $199.
After your 1st receiver (lets say, for example, you get an HDDVR, and 2 regular DVRs), each additional receiver, be it HD, DVR, or Standard, is 4.99 a month. This is a fee to mirror your programming for your package to each receiver. On your bill, its called a "lease fee", but its not a lease fee, its a mirroring fee.