I use a
D-12 standard definition receiver with the 18" dish.
I have never tried using a high-def receiver with this setup, but it should work as long as you tell the box that you are using a 18" dish with an LNB (can't remember the exact wording but you don't want to use the SWM setup. I think it is something like multi-switch.)
When I plug it back in at home, the receiver sees the SWM setup and automatically reconfigures itself for home.
If you wanted to buy one you'd have to lease it from DirecTV with a new access card. I just pull one out of a bedroom that I keep around for camping.