JPIII:
Try windshield washer solution as a thinner for the craft paints and use it to clean your airbrushes.
I am finding out that the larger cans of spray paint like offered by Kryon works great for painting plastic buildings and has a long shelve life and its cheap in comparison to Testor's and other spray paint products. Its funny that we as modelers will buy a weathering solution that is a 16 oz. or so bottle and pay $10.00 + tax, when you can make a similar product for a lot less with nothing more than rubbing alcohol and India Ink.
As they say, "Necessary Becomes the Mother of invention". Look what earlier railroaders like John Allen created by using off the shelve, non-model railroading products and materials!
My 2 cents worth.
Greg