steve, here is my thinking on this, what will it be worth to you?
if they think its worth more than that pass it up, there are many posts that are in the forum which can give you an Idea as to what the value of certain components may hold, you will also have to figure your time, chemicals and other costs, there is also the waste you generate, this also costs some to treat and dispose of properly, so especially when you first start out having them to pay you to take their scrap would be the best price to pay, after you have got the processes down and learn to make your own chemicals as much as possible, maybe you can charge them less to haul off their scrap.
now when you get a few gold buttons under your belt you will KNOW how little you will be willing to pay for it, if I have $$$ and want to buy I buy from a trusted coin dealer and local gold buyer who sells me karat gold for melt value, and if the green money goes down my gold goes up, I am not a buissiness man and money has never meant much to me if I have food for the table, but I like the Idea of putting some of that yeller metal up so that I may keep food on the table, so others may have better advice on the buisiness end. I do know when first starting out you can spend more than you make in this, but a stick to attitude and doing your homework can be fun and slowly rewarding, besides very rewarding when you melt that pretty yeller metal you worked so hard for.