Cost of product add-ons linked to product variation

I am looking to build an online checkout for my Scuba Diving company.

We sell three types are diving:

• 2 Tank dive ($$100)
• 6 Tank dive ($250)
• 10 Tank dive ($700)

Some customers will need to hire equipment from me and some will not. Depending on the number of dives they buy this will affect the number of times they will need to hire the equipment. I charge $5 for each dive they do, so if they select the 10 dive pack and then click a checkbox for dive equipment hire, then I’d like $50 to be added to the cart.

I realise I could achieve this by creating another 3 product variations and adjusting the prices accordingly, but we are likely to add additional options in the future such as dive computer rental or camera rental, This would mean the total number of variations would get out of hand.

So… As the title of the question says, how can I link the cost of an add-on to a particular product variation?

https://www.ads-software.com/plugins/woocommerce/