I run a silent disco company.
I want people to hire headphones from my website in any quantity.
I want people to select between a 2 channel and 3 channel option.
I want the 3 channel option to add £39.99 to the total price.
E.g. - somebody books 100 headphones at £1 per headphone = £100.
Somebody books 100 headphones with 3 channels at £1 per headphone = £139.99.