Hi,
We've worked on an app that allows you to automatically have your products tagged based on conditions like type, vendor, price and even stock availability.
Smart Tags: https://apps.shopify.com/smart-tags
Think of it as automated collections (smart collections), but for tags!
We've been using it for a couple of months for a client's store and just submitted it for review.
Would appreciate it if anyone would be kind enough to spare some of his/her time to take a look at the app, and for any feedback.
It has a forever-FREE plan that anyone can use.
Thanks!