I'm not trying to be difficult but the order form you are describing is not complete.
Column B is the fabric.
Columns D-G will provide the cost for each size, which will be filled in using formulas that look up the prices from a table where you have all the prices for everything.
But where/how does someone enter the quantity of each (or any) size they wish to buy? It cannot be done in D-G because they have formulas in them.
Consider this instead:
Column B is the fabric from a popup menu
Column C is the size from another pop up menu (S, M, L, XL)
Column D is the price for one shirt of that fabric type and size, which is filled in using a formula that looks up the price from a table that has all the prices.
Column E is the quantity desired
Column F is the total cost for this row = column D x column E