attributes question

[tedbooks]

i am making a shop that the products have a long list of attributes about 30,

customer can choose the first 4 for free and the rest they pay $2.00 each

 

i have addes the product_option from chandra so now i can list the options as a checkbox which makes the choosing of multiple attributes easy but how to make the first four for free is the hard part.

i wanted to avoid having the extra 30 check boxes.

ps.we don't know which option is free just the first four that the customer adds to the basket

 

if some one points me in the right direction and atleast to how the item is added to the basket where i might adjust the price of the product including the attributes