Hi,
With HikaShop, you can use the variants to have different sizes, colors, etc.
The limit is that the values are fixed by you, and not by the customer, so if, for example, you have sizes 10 / 20 / 30 and the customer wants 25, this size will not be available. If you use custom fields, the price will not be calculated automatically.
So, you will need a plugin. A plugin based on custom fields which will update the price depending on the values in these custom fields. It require PHP knowledges to make this kind of plugin.
Here is a link to the documentation:
hikashop.com/support/documentation/62-hi...r-documentation.html