Thanks for all the good insight!
I have created a table called OptionPrice
With your example setup:
PriceID (PK) auto increment, ProductID, SizeID, Price
I have inserted some data in to this table
(1 ) first record in table
(48) product id for a t shirt
(5) sizeID which is x large in Size table
(5) price of £5 if this option selected.
What is the next step to making this work?
Is the php needed to increase price in shopping cart complicated?