Increase price using checkbox

[jesper03]

Hi everyone, I need to add a new checkbox right under the price box that allows me to increase the product's price by a certaing amount (i.e 5$).

The only constraint (unfortunately) is that I cannot do this using combination since I changed the way my shop shows the combinations and adding new ones can cause me problems.

Hope that someone of you can give some hints.

Thanks in advance and have a good day.