How much you need can be partly determined buy the color or the colors ability to cover the primer. I could see yellow,whites and some reds using abit more given that most manufacturers have cut out most if not all lead from their paint lines. I would say a color with average hiding you should be safe with 6 ltrs...depending on the mixing ratio you could have up to 9 ltrs of sprayable product!
For anyone who's wondering about being able to buy single stage paints this year....you should be able to get it. Manufacturers and retailers will be able to sell till the end of 2010. They will not be able to order new stock after July so, if they run out of one toner needed to make a color after July....you won't be getting a mix.
Anyway, most paint manufactures have or will have VOC compliant single stage lines available by that time. They might just a little different to spray than whatever you are used to....still will be fine tho.
Our world won't come to an end just yet.....however....there are people working on it!
