Inventory question

I'm opening a store where I sell variations on the same product. Basically there's the basic product, but for an extra fee it can be painted, then for another fee it can have finishing work done, etc. The extra options stack like this:

Unpainted base version - $20
Painted version - $30
Painted version w/ finishing - $40

Right now I have them listed as different variats on each product page, but that makes inventory tracking difficult since all the different options start with that unpainted base version. Is there any way to set a single master stock quantity no matter which variation someone selects?

There's no way to do this within Squarespace unfortunately, you'll need to use an inventory app like Trunk

Trunk can sync inventory in real-time between the same SKUs. If you give all your versions the same SKU, Trunk can keep them in sync within Squarespace. If one sells or changes in stock, it will also adjust the others.

Trunk also supports bundling/kitting/components which allows you to create a master product. Then your other products can depend on this master product in various configurations (e.g. if you're selling pencils, the master product is one pencil, and then you can have packs of 5, 10, 15 depend on this pencil).

Please let me know if any questions, I'm the developer!