Custom field that behaves as secondary Quantity

[john-doe]

Greetings. I'm blocked in the way that i need to set a custom field that behaves as a secondary quantity.
The problem is i set a simple custom field like in 2.66 where i ser 1 is 35$ and 2 is 70$ but in the front end appears 2 lists of the same issue when it should be one list with all variants.

Or how could I set up the custom field in this case since the mechanics changed from 2.66 to 3

Thanks in advance
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