What is an "HDTV compatible" TV?
Can the screen support 480 resolution?
Can the screen support 720 resolution?
Can the screen support 1080 resolution?
Progressive or interlaced?
Must it have a digital demodulator?
Must it support the digital type of connections required to transmit HDTV at its max?
Does it support CableCard?
There's a lot that could be considered "HDTV compatible" so you'll have to be more specific here. I recommend you at least get a TV with the ability to show at least 480i and 480p, and preferably with a built-in digital over-the-air tuner.
Over-the-air is something you may want to consider if you can't afford digital cable at the moment. Just use a UHF antenna, hook it up to your TV's digital tuner (or digital tuner STB), adjust it, and you're ready to go. The quality does not degrade or get fuzzy like analog, so as long as your signal bar is 80% or so, you'll get a great picture with no cut-outs, at least in my experience. With less you will start getting blockiness and pauses.
As far as digital TV goes, the mandates are only for over the air broadcasts so far AFAIK so you will still be safe with analog cable for the time being.