We have created a shopping cart that will allow the shopper to purchase "T-shirts". Each t-shirt comes in various colors and all t-shirts come in the same option of sizes. *The sizes offered are small - 5XL. *Sizes small - XL are the same price and 2XL and up are an additional $3.00. *We would like to know the best way to accomplish this type of shopping cart set up and functionality, create a rule, dynamic drop downs etc?