I deal with Bishnupuri Silk sarees in my Fb page, price = 3599/-
When user pays online, we offer discount of 99/-, so the effective price to pay becomes: 3599 - 99 + 100 (ship) = 3600/-
When user opts COD, the total price become 3599 + 100 (ship) + 50 (cod handling fee) = 3749/-
I need to implement this business logic in my site .. how do I do that? Plz suggest me in details