The PC Electronics TVC-9S is a very nice downconverter, and I'm glad I bought one, but it is a bit expensive. To really make it easy to get started, I think it would be great if something simpler were available.
North Country Radio make a VCO controlled 33 cm downconverter. I haven't tried it, though, and my one worry is that without a frequency counter, it might be tough to tune. It depends on how much tuning slop your ATSC tuner will allow. But on the other hand, their downconverter is a third the price of the PC Electronics one.
One thing I think that could be changed is that these downconverters are designed to shift 33 cm down to VHF low. That means their mix frequency must be very high - in the 800 MHz or so range.
For DTV, I don't think it's necessary to chose such a low IF. If you picked a mix frequency of, say, 421 MHz, you'd wind up with 909 MHz being output on TV channel 17. That would be ideal for around here, because channels 15 through 18 are unused (since 16 and 17 are used for land-mobile in San Francisco).
So, dear readers, if you can design a cheap crystalized or PLL controlled downconverter to go from the middle of 33 cm to the lower end of the UHF TV band, please let me know - I think you could make a lot of hams very happy.