http://www.cleanenergyfuels.com/news/2012/11-1-12.html
Currently priced up to $1.50 a gallon lower than gasoline or diesel depending on local markets...
I am currently in the process of getting my own CNG station up and running. The last numbers I saw on natural gas prices was something around $3.00/M . According to this chart, the current price is something in that vicinity.
Given that the "M" refers to a thousand cubic feet of gas, and since a "gallon" equivalent of natural gas is about 120 cubic feet, then the price per gallon of natural gas out of the pipeline ought to be about $0.36/gallon.
Add on to that a nominal pumping cost and you are probably looking at 40 cents per gallon.
Multiply times 10, and you get $4.00/ gallon, which is what Diesel is selling for in a lot of places right now.
Your gas price link, residential price is about $20 per thousand. $3 is a trading price not a consumer price.
Natural Gas then compressed to over 3,000 psi at a vehicle fueling station is going to be around $2.00~$2.50 per gasoline gallon equivalent. Possibly more in markets like California.