I lucked out with mine. About two months ago, I picked up the last RCA DTC-100 in Miami. As late as January, they were widely available in Radio Shack, originally for $549, but they eventually dropped to $199 when that model was discontinued.
I called every Radio Shack in the city, until I finally found a store demo in a backwater store that the manager had thrown in his office. Considering that most STBs are $500-800, I thought it was a steal. It's a DirecTV receiver, but you can also connect an antenna to pick up local over-the-air HD channels.
The biggest drawback (which is probably why it was discontinued) is that it has a VGA output, instead of component. I paid an extra $50 for a VGA-to-component converter, and so far, it's worked flawlessly.
Aside from that hard to find gem, I think there's a Zenith OTA HDTV tuner that's recently dropped below $200, but that doesn't get you HD DirecTV broadcasts, which is about to double its HD channel line-up next week.
