Sadly, no, it’s not possible to update collection items with the CMS import.
If you are technical enough, you can use Webflow’s API to do it.
I’m currently building a solution for those who are not technical enough to use the API. It allows people to update their collection items by uploading CSV files. If you want, I could help you import your prices later using my tool.
Were you ever able to finish this solution? Interested in learning more about being able to append data to an existing collection through a csv import.