Forum Academy Marketplace Showcase Pricing Features

Alternative to Repeating Groups?

Basically I need my users to select Products which are displayed in a Repeating Group. They then go to the repeating group, enter a Quantity next to each of the Products they selected above and it totals how much it’ll all cost with a grand total appearing outside the RG courtesy of the Extractor plug in.
The problem is that I can’t find a way of referring to the Input where they type in the Quantity of the products so I can’t record the transaction successfully in my data. I can’t find a workaround despite useful help on here.

So can anyone point me to a “model” of a shopping cart where people can select products, specify a quantity and have it save an order in the data? I’ve been going back and forward for weeks with this design problem and I think I need to change direction but don’t know a way forwards despite watching seemingly endless videos, reading the manual and this forum etc.
I’d really appreciate a nudge in the right direction.