Price by Formula Calculator for WooCommerce

In a Number field type, I would like to offer the user a choice of 1, 5, 8, 12, etc.. This does not work with a minimum, maximum, and step value, because the interval varies.

So I tried changing the field type to Select, but now it seems that the option values are no longer recognized as numbers, but as strings, so I cannot perform calculations with them.

Is there a workaround or a feature update possible?