You can buy McGuiars wash (the best in my opinion) and get many washes per bottle. It's definitely cheaper to use and superior to the SPNG product. That's why they have the market share lead in car care products. At only 8 washes per sponge, the price of the SPNG car wash sponge is almost $2.50 per wash.
We are apt to shut our eyes against a painful truth... For my part, I am willing to know the whole truth; to know the worst; and to provide for it. --Patrick Henry, Patriot and Hero of the American Revolution