Hi Alex, 

There isn't an option to show the price there if it is 0, as when it is 0 it is hidden on the front-end. You can try showing it with adding custom CSS. Please try adding this CSS to the page:

div.am-category-service-inner > div > div > div > span:nth-child(2) {visibility:unset !important;}

and let me know if it helped. 

If you don't have an option to add custom CSS to pages, you can add it as format HTML : 

<style>
div.am-category-service-inner > div > div > div > span:nth-child(2) {visibility:unset !important;}
</style>

You are welcome. 

There are a lot of users that don't want to have the price shown anywhere on the front-end, so this is why when they set it to 0 it isn't shown at all. You can suggest this as a feature request here, though.

If you have any other questions or concerns feel free to open a new ticket and we will gladly help out.