That is a personal thing for you and the refiner.
Not many will post their rate or agreements with customers.
2 grams per kilo is about what you get from fingers if i'm correct. Compare it to what you can get for it as scrap on e-bay.
Are you interested in selling them, or are you set on toll refining them? Most people are reluctant to post their rates, as it could affect their pockets. @Martijn has a point, ebay is a good option although they take a pretty good chunk from the sales. I've bought fingers from there myself.
I'd do it for the low. - cost of chemicals and percentage of the gold recovered could be negotiated. Because I just like to do it. So I wouldn't charge much.