Just a word of caution: I know shops around the country charge supply charges and many business seminars promote this, but depending on local and state laws (AND, I am not a lawyer), any charge on the invoice has to backed up by a formula used to determine the charge. In other words, in New York you can charge a supply charge, hazmat charge, etc, but you need to justify how you arrived at that number. A few shop owners I know got fined because they were charging an arbitrary percentage.
I called the NY DMV, and according to them, you need to show how much in “supplies” you use per job, how much you pay for hazmat. You can recoup your money, but you need to justify any charges on the invoice.
I am just bringing this up so shops can be carful and find out local laws.