Text editors

I can make such a button (next week) to htmlarea (default editor of moodle 1.9.X) or tinymce (default editor of moodle 2) but you should really be cautious of terms with these licenses:

3000 daily equations rendered does not mean that your site is using 3000 equations.

If you visit codecogs editor each rendered equation is a different equation. When you edit notations you can easily render 10 different notations while writing - usually you don't have that notation ready with one click. If you copy those images as images to your site or if those files are read from site cache they don't cause new requests to codecogs server.

Suppose you need 10 equations where image is read from codecogs server to your moodle and you have 100 visitors who read your equations once/day - it means 1000 rendered equations. If your visitors read those pages 3 times/day it means 3000 rendered equations.

Suppose that you allow your visitors to use a plugin that calls codecogs server and each visitor needs 10 clicks to write one notation/user. It means 1000 equations. If each of them wants to add 20 notations to your moodle - they may also need to edit their texts and notations - you will pay for 20000 daily equations rendered...