I personally wouldn't let it go for less than 1 to 2.5k at an absolute mininum. My reasoning is that you will need a convertor box to see HD signals on a non-HDTV set.
HDTV hasn't taken off because of outrageous price tags and lack of media. HD-DVD will debut in March. The XBOX 360 is capable of producing a High-Def signal, now (games and video will come once a HiDef media is incorporated). HD is only recently debuting in some cable TV stations. The PlayStation 3 will use Blu-ray discs and support High-Def gaming and video media.
The name, as a brand, actually has lots of possibilities.
HiDef will be big, and there will be many that will be on the outside looking in for a while. But, I think if you hang-on to it too long you will have messed-up your chances because this will be a temporary window. Eventually, everyone will have an HDTV. After that it will probably be a great DVR name for HD movies, though. But the value in this name is the brand, as you won't find people searching for HD and getting relevant results, I don't think.