I've got two Venstar Thermostats with Insteon Adapters for sale. They are the 1-day programmable ones, not the 7-day (what's the point when you're going to hook it up to Indigo anyway, right?)
MSRP for the 2 setups looks to be about $490 (although on sale at Smarthome for about $370 right now). I'll gladly sell the whole setup (2 thermostats and 2 adapters) for $200 obo.
Let me know if you have any questions.