there are lots of possible ways to do this, depending how many product option combinations you require
for example, for each SKU, is price dependent solely on size, for all items, or do other options have an effect ?
eg is a red t shirt in xxl the same price as a black one in xxl
you could have a separate price table with the combination of option id's having the unique price for that particular combination.
if you are confident that price is based on size only, you could even add it to your size table
Also, if you are considering different prices for the same SKU, you may need to show 'price from' or a price range.