Hello @Jeff_MarcheHave you got the solution? As you want your customer to select the quantity from all variants of a product and want to calculate the price depending on the selection on quantity then you can try the MultiVariants - Bulk order app.
You need to create a product in Shopify and create variants that will be visible on the product page under the main product. Applying MultiVariants, all the variants will display under the main product and there will be a quantity selector for each type of item. Your customer can choose their own combination of all products. And when the customer enters any quantity for the variants, the price will be updated automatically. You can decide whether you want to just show the total price of all variants or the total price of each variants also.
With this app, you can set the minimum-maximum restrictions for variants, so your customer must choose a quantity from all the available variants before going to the cart page. Additionally, through this app, restrictions for minimum-maximum quantities, predefined bundles, interval quantities, limits on variants and orders can be achieved. These restrictions are also applicable on the cart page.
If you’ve different criteria for different products in your store, then you can set rules according to that also. You’ll get 3 days of the trial along with excellent customer support for exploring all other features.