Buying a DVR

I rent an apartment that includes Direct TV service and was wondering if I can buy a DVR myself and replace the current box. If Yes, do you have any reccomendations? It doesn't have to be new or an extremely large hard drive. I'm not looking to spend a bundle.
My landlord is cool...but has zero understanding of any electronic equipment, so I'm trying to handle this myself.

Thanks for your time and consideration.

Tim Hughes
Long Island, NY