Customers need to choose any 4 items from a group of 10.
No more, No less.

This has to be displayed as one product. ($120 to pick any 4 items from the list)

So far I have set up a check box attribute with 10 values but I don't know how to limit the choices to only 4 and I don't know how to validate so that there is a minimum of 4 selected.

What to do??