Uhm, the "Catalogue mode" turns off "Add to cart" buttons only, anyway. So that's not it, of course - sorry.
Then there are two "Display price" switches in the backend:
1. Under System -> Configuration -> Display tab -> Parameters for products (for price display on product pages)
2. In "Content menus" and "Content modules" configurations for product listings, and there again under "Parameters for products"
Make sure they're set to "Yes" everywhere.
If that doesn't help, prices were probably hidden per CSS (Firebug or similar would prove), or per code modification in PHP files.