I've been concentrating on the ATSC repeater output all this time and have neglected considering the user uplink side of the equation. In a single e-mail with the SR Systems folks, I think I see the way forward.
NARCC, the local repeater coordination body here in Northern California, has not been friendly to ATV in the 70 cm band. And you can't really blame them - it's 6 MHz of real estate that is sorely needed for other things. The big problem is that generating power at 70 cm is vastly less expensive and easier than for the higher bands. Given that state of affairs, it would be very, very nice to be able to use 70 cm as a user uplink band for a DATV repeater.
Well, it turns out that according to Stefan, the europeans have had great success with DVB-S in a 2 MHz wide bandwidth at about 2 mbps encoding! That's excellent news! I'd be shocked if we couldn't find a 2 MHz channel somewhere between 420 and 440 MHz for this.
Not only that, but the DVB-S encoder board is less than half the price of an ATSC one. That means that a user station can be had for €590. Add to that the cost of a Downeast Microwave 7025PACK and you're on the air with about 8 watts of transmitter power for just over $1000! That's not bad for digital ATV!