Depends on your definition of "reasonably priced."
The Hughes E-86 can be had for $400ish, and works pretty well. It's main drawback is the fact that it will only output 1080i (either native from HD stations or upconverted from 480i for non-hd sources) thru it's component video output, and the upconverted 480i is pretty nasty looking. It can pass 480i natively for your set to line double, and this looks much better, but it will only output 480i via S-video. It won't do both simultaneously, either, you have to switch modes on the box, then switch inputs on your tv.
Newer models from Sony and Zenith (same box, built by Zenith) will pass any scanrate via component video, so you only have to switch the box's scanrate with the remote. Their 480i to 1080i upconversion is also said to be much better than the Hughe's box. These run $700 to $800 though.
The old RCA DTC-100 can be had even cheaper than the Hughes, but requires an optional adapter for component video--has no component video output on the box itself. Many people own this 1st generation model, and are quite happy with it.
Another mfg to check out is Samsung.
There's a very active HD-Hardware forum over at AVS worth checking out for more specific information on stbs.