Nope, it really does cost only around $25, maybe $35, to include the HDTV Tuner. In 2004 there were standalone HDTV tuners being sold at $149, with a list of $199. And this price had to include a cabinet, separate power supply, all of the output connectors, the box, the extra manufacturing cost, and all of the cost of inventorying, shipping, and marketing the box.
There is a HDTV tuner card for PCs that you can buy for around $80. And that still carries the extra cost of having to have additional circuitry to interface to a PC through a PCI bus, and all of the marketing cost and overhead of a standalone product. I suspect the HDTV tuner chip on that card cost about $10.
The HDTV circuitry is quite commonplace now. And very cheap for Asian companies to manufacturer. No R&D to speak of to recover. No way it costs anywhere near $250-$500 to include.
Witness that Panasonic took their 43" LCD RP TV, added other functionality to it, improved it, increased the size to 44", threw in the HDTV tuner, and cut the list price by $500. If the HDTV circuit cost them $250-$500, there is no way they could have enacted a price decrease of that magnitude.