Access Access 2010 report summing

[mkssolutions]

I have a group report that will produce an invoice. The amount billed on the invoice is at the product table level, however, I need to show the individual item table records that make up the product. I then need to total the amount of the product, amount paid, and amount due. However, the sum of these fields are being multiplied by the number of item records. How can I sum only the product table field? Here's an example:

Product purchased is $100
Product contains Item 1, Item 2, Item 3 listed in the DETAIL band with no dollar amount
The Footer needs to show: Total due for Product = $100 (winningbid)
Total Amount Paid = $0 (amountpaid)
Total Amount Due = $100 (amountdue)

GRAND TOTAL DUE = $100 (sum of grandamountdue)

BTW, a customer can buy multiple products that will appear on the invoice. And, what is showing on my report is $100 winningbid, $ amountpaid, $100 amountdue, but grandamountdue is $300.

Any help is appreciated.

Thanks