Need a DVR hard drive

I finally jumped on the HD bandwagon for my Dish TV, and turns out my receiver has a DVR included, but it needs a hard-drive to function (which makes sense :S) It needs about 500 GB minimum, and I don't wish to spend a great deal of money on it.

Also, I'd prefer it to be a plug-and-play easy to use model, as my family is a little... technophobic.