How to sort posts by price

Unfortuntely, this is probably not a job for a beginner. In spite of how simple it sounds, creating a button to allow a custom sort requires quite a bit of coding.

As an example, here is the code for a ‘simple’ form to allow selection of a category and sort order: https://wordpress.mcdspot.com/2012/09/21/simple-form-to-select-a-category-and-sort-order/

Witch fields require changing so the search shows posts by value – price?

You will probably need to hire someone to do this for you. You can post a job request on jobs.wordpress.net at no cost for posting the request.