Show the Price as €/meter

Hello,

I'm looking for help from someone more experienced then me. I need to show the price in the product description page (and also in the product listing pages if possible) as price per meters so it looks like this:

5€/meter

I know I can set this to show with all my products when I use €/meter as the symbol on the right but I need this to show ONLY in some of my products/categories. I guess this can be somehow done in tpl_product_info_display.php?
I've also tried to add the word "'meter"' just behind the quantity box in the product description page but I don't know how to show this only on some of the product pages. I added it to the code in tpl_product_info_display.php

Can anyone help?
Thank you.

Daniela