Hi,
If all your products need to have the same text after the price, then you can simply use a translation override of the default text there, which is "each".
Here, we explain how to make translation overrides:
www.hikashop.com/download/languages.html#modify
If you need to have different text for different products there, then you want to use a custom product field and a view override as explained in the "I sell packed products, how can I change "each" text in the product page ?" section of our FAQ:
www.hikashop.com/support/documentation/106-faq.html#tran