I need a customisation to the Inventory (Product & pricing setup) in SquareSpace

Existing SquareSpace functionality needs customisation to enable prices to be added against optional extras and total cost to be recalculate on the selection/de-selection of an optional extra.

This could be achieved via the field setup on the 'Additional Options' form?

We are currently using the Adirondack template in Square space, i've attached some screenshots of the product setup:

1. setting up a product

2. an example of one of our products - TILLSTAND 600MM
- user selects the product and finish (Plain, or Feature) they require
- the basic price is calculated at this point

3 & 4 Form - Additional Options form
- its here i'd like to add the additional options, on selecting/de-selecting an option the basic price is recalculated accordingly -

*this is the change we require*

- So when setting up a field on this form, id like to (optionally) be able to add a price

- When the user selects an additional option the price is added to the basic price already selected, and the total price recalculates accordingly, likewise if an option is de-selected or changed the basic price needs to recalculate.

eg.
TILLSTAND 600MM - Plain Finish, Cream + Black edging £90 (basic price)

+ Rear Drawer (£35) - basic price recalculates to £125
+ Solid Doors (£20) - basic price recalculates to £145

- User changes their mind and removes Rear Drawer (-£35) - basic price recalculates to £110

- User checkout - Total price £110.