There used to be a ton of Chrome extensions that did this, but now they all charge a hefty monthly fee. Are there any other tools that do this?

There are several areas where you can find similar solutions:

Services with free or freemium plans that show analytics, mentions, subscriber growth/decline, and other metrics;

Tools with one-time fees or "pay only for what you use" instead of monthly subscriptions;

Open-source projects and local solutions that you can launch yourself without a mandatory subscription.

This problem is truly widespread these days. Alternatively, you can consider web services that work without installing extensions and don't require a subscription. There are solutions who follows who instagram which allow you to track relevant changes or actions through an external interface and eliminate the need to pay extra for monthly access to browser add-ons.