in the query driving your combo box, include the prod rate in the third column.
so if your products table is this:
Code:
tblProduct
Primary_Key Prod_Name Prod_Rate
1 Product A 5.00
2 Product B 10.00
3 Product C 15.00
the query driving your combo box would be
SELECT Primary_Key, Prod_Name, Prod_Rate from tblProduct
Then on your form (assuming it's a non continuous form) just put a text box next to your product combo box and put in the CONTROL SOURCE property: =cboProduct.columns(2)
where CBOPRODUCT is the name of the combo box and 2 is the index of the field you want (Prod_Rate is index 2, combo boxes, list boxes and arrays start with an index value of 0)