I've been testing this plugin during the beta for awhile and I must say it is amazing ! .
it is kinda like 3ds max State sets, expect it works : )) with many additional features of course .
There is no official info yet about the price, but according to the developer there would be an option for both perpetual and subscription license.
Check the link below for more info
https://renderstacks.com/and here is a sneak peak video to see it in action