If you are planning to use 2 DVR's plus a 3 box you are going to have to use an open face antenna just like the one on your house. You can mount this on a tripod and take the time to learn how to point it. I would recommend that you get a SWM SL3 antenna as you would then only need one coax cable running to each receiver. Just be aware that none of the dome (portable or roof mounted) will have enough connections available.
Winegard also has a roof mounted fully automatic antenna that would allow you to connect all of your receivers.
$200 actually sounds like a bargain to me considering the amount of wiring that will need to be run, but I doubt they would actually do it once they found out what you actually wanted to accomplish.