[PlasmaKrab]

To take things from the beginning (sorry, folks, time zones and all that):

-Small arms thermal sights exist in US services since some years (think AN/PAS-13 series), now IDK how current they are in field units.
-There may be an issue with thermal vision range, i.e. there is no way in the game to have thermal vision reaching at less than 2km (several times the range of an infantry squad's small arms). If there was a possibility of having TI with a range of 500m or similar, the cost difference wouldn't be as huge. Now I guess there is no way to change the way vision types are assigned, so that's that.
-Unit cost is only related to unit capabilities. AFAIK there is no way to link unit cost to a specific OOB. Identical units with identical morale/exp ratings have the same cost over all the OOBs. I'd say we need to stick with that rule in order to prevent too large game imbalance.

Thinking about it, it could be interesting to restrict full-range TI to the leading unit of an infantry platoon. That would mitigate the cost issue and provide the long-range recon capability discussed above (up to the arty call ability). Now I don't remember that US platoons use a dedicated command section of any sort, so that may not work in OOBs 12 and 13.