'NASA finds lunar ice. Says, "ok ready for aggressive mars program. Somebody sell us some fuel at luna. Somebody? Anybody? Hello? Is this thing on?" '

Say one needs to lift 20 ton to lunar surface in order to mine 20 tons of water per month and say for each additional ton landed on the moon your production can increase by 2 tons per month.
Now, assume there is an average demand of 100 tons of fuel per year for Manned Mars. Assume it takes 200 tons of water mined on lunar surface to get 100 tons of rocket fuel to high Earth orbit to be used for Manned Mars. In addition assume there is demand for additional 200 tons of lunar water per year for activities other the Manned Mars missions.
With 20 tons capacity in a years' time you produce 240 tons, assuming each ton is sold at 2 million dollars at lunar surface at point of production ($1000 per lb about 1/10th the current cost of shipping rocket fuel to the lunar surface); this gives a gross yearly revenue of 480 million dollars. Obviously you won't make a profit in the first year-
The shipping cost alone for your initial 20 tons would be about 400 million (at $10,000 per lb). In addition assume the price of lunar water could drop to about 1 million per ton in the next 5 years- giving you half the gross revenue at starting production levels. Also assume that if lunar water is selling at 2 million per ton at lunar surface, then the price of this water at high earth orbit will about twice this price.
Now, assume one location with minable water is roughly 10 sq km and assume different concentration in this area- say 20% of weight of first meter in depth can be extracted in a total of 1 sq km and about 10% in other 9 sq km. The 1 sq km at depth of one meter (and there could be on average several meters of depth to mine) has a total of 200,000 tons of water- and assuming an average price of $200 per lb of the water extracted, the highest concentration area has gross worth of 80 billion and might require 10 or more years to extract.
The cost of increasing production capacity and operation cost can lower exponentially- selling water and making rocket fuel will lower cost of getting to the Moon. It also lowers the threshold cost of other operations- such as mining iron ore, which also increases the demand for water and allows one to buy some equipment made on the Moon at a lower cost than shipping it from Earth. In other words, with open market, competition will drive down price/costs, and even though you are in a highly deflationary market, you can make huge profit- though you can also lose your shirt if you aren't lucky and/or smart enough.

"I really don't see commercial interests doing their own space program on the off chance that they might be able to sell something to NASA if congress will let NASA buy any, by the time it's available."

The commerical interest is not in fulfilling NASA's needs- this is the current situation. The commerical interest will be in developing markets for consumption of the private sector. For instance, harvesting energy from Space and delivering it anywhere on the surface of the planet has a huge market potential- and could be so comprehensive, that one day it's an option instead using batteries for small devices, or automobile (or flying vehicles). Or another example is in making new materials- simple stuff like stronger steel, or even things in the nanotechnology area.
Mining water in space is similar to mining crude oil on Earth- this lowers transportation cost which allows other activity to be economical.