I'm trying to create a product with various options, but I want each option to be able to have a number entered. For example:

Product comes with 1 dvd set and 6 softbound books. I'd like to have the options as follows

# of hardbound upgrades - +$5
# of extra softbound books - +$20
# of extra hardbound books -+$25

There could be up to 6 hardbound upgrades, and unlimited extra books. How could I do this? Thanks!