@luminus
Thank you for the reply and for the Health Check plugin (maybe this will come in handy again in the future).
I am afraid that the theme that is used causes this problem. Because with all plugins (exept WC) turned off the prices are gone as soon as this theme is activated.
This theme did get a new version today, but I am not looking forward updating the theme since I made some changes in it…
And about the replaced files of WC, I don’t know what happend then, because the files were in wp-content/themes/mytheme/woocommerce/.. And we did not restore any old backup