'required'

-- HikaShop version -- : 2.6.4
-- Joomla version -- : 3.6.4
-- PHP version -- : 5.6.27
-- Browser(s) name and version -- : Chrome 54.0.2840.87

Each product has 3 sizes. Each size has a different price.
I can create variants or options to achieve this.
But variants or options can't be made 'required'. Correct?

I know custom fields can be made 'required' but custom fields can't set the price in the cart. Correct?

If the choice is between three prices
Select
Small
Medium
Large
How can I make sure the buyer doesn't leave it as 'select'?

Hi,

A characteristic is required ; because the combination must match with an existing variant.
Options are basically not required but with a little custom plugin, you can force it.

Regards,

But if the existing variant is "select" then the buyer might leave it there and not select a size. True?

If you have a "select" variant that is by default, then yes, that's possible. But in that case, set it with a quantity of 0 and make sure that your turned on the "display out of stock products" setting of the HikaSop configuration.
That way, the select option will be the default one in the dropdown, but the add to cart button will only appear once one of the other variant will be selected.

Yes. That works. Thank you.