If the variant price is different that the main product price, it must be set on the variant attribute, not on the product variant.

Try manually : in Odoo 10 open a product which has variants. Upon the form, on the left, there is a button "price of variant" (or similar). The button open a new view with the list of product attributes (which are responsible of variants automatic creation). You can set  a surplus price on each attribute. Beware! that surplus price will be the same for each product using that attribute.

Now you can try to import : go to Sales / Configuration / Products / Attribute values, export the list (don't forget the name field, it is mandatory to import). The price is stored in the `price_extra` field. Add your surplus price and reimport.

You can export and import variant prices out of the products (not product variants)
Take a look here, it's in French

https://www.youtube.com/watch?v=-5j7SIriwZ0&t=607s

You can also configure specific variant prices in the pricelists, without using price extras per attribute. Users may need both ways to manage their pricing.