LAN Hard Drive for "WD TV"

I just got a "WD TV" and I am looking for a hard drive for it that everyone in my house can add files to over the home network. The plan is to have the "WD TV" and the LAN hard drive be behind the HD TV in the TV cabinet. It has to be able to handle being accessed by USB and LAN at the same time. (aka I can watch a movie file while my brother adds a new music album he ripped from the store). The RAID NAS solutions seems a little extreme and out of my price range. I would like to spent $100~$200. Does anyone have any ideas?