You knew I'd say "it depends" didn't you?
The receiver is available at Camping World for $100. (You might find a used one on Craig's List for less.)
Next you have have to have the satellite dish. Which one of those you want depends on your desire to have an "automatic" system or one where you have to learn to "point the dish" (at the satellite) yourself. The latter can be had (used) for less than say $50.
If you want automatic, the Dish Traveler is very popular. It's light, small, and self-contained. You just set it outside in a place where it can see the satellite. Put the coax on the jack. Follow the setup procedure on the receiver, and in about 10 minutes (of waiting for it to do it's thing) you'll have hi-def TV. That will set you back about $350 at Camping World.
Of course you can spend more and get something that will track the satellite continuously while you drive down the road.
Oh...and the min charge for 30 days of Dish programming (120 channels) is about $50 + taxes & fees.