This article explains how to /month text after the price e.g. like this

You can edit price field via Vehica Panel > Custom Fields > Edit “Price” field

Set “Text before value” and “Text after value” e.g. “/month”

You can also have multiple price fields e.g. one for full price, month rent, day rent etc. You can add new Price field this way:

then drag-and-drop it:

It will be available on the submit listing etc.

You can also add it on search form same way as any other fields