olddude: Buy a battery capable scale with a usb port, make up or have someone make you a spread sheet to feed your scale data into - bingo you have a total to pay out without playing all day long with numbers.

You may even be able to find some open source POS ( Point of Sale ) software that will do the job for you.

People can not relate to your $5.00 offer whereas they can at $0.09 cents a pound. Put your laptop and scale to work.