I have looked up a couple of examples of "no frills" digital TV converters and they are not yet on the market.
Examples of Basic Digital TV Adapters:
RCA DTA800
Zenith DTT900
You can use older, first or second generation non-activated HD Satellite TV recievers, they also have a built-in over-the-air digital tuner and they have the right connectors to “downconvert” them to an older television. You don’t have to actually activate or pay for the “satellite” part - you can just use the digital over-the-air tuner in it.
I don’t think those qualify. For a tuner to qualify, it cannot output any high-definition signal:
Disqualifying features:
Outputs (General):
Digital Video Interface (DVI);
Component video (YPbPr);
High-Definition Multimedia Interface (HDMI);
Computer video (VGA);
USB IEEE-1394 (iLink or Firewire)
Ethernet (IEEE-802.3)
Wireless (IEEE0802.11)