There is a sales thread about that on this forum, it's cheap and decent enough, although it's not updated since january
And where do we invest? That was the question in the first place.Easiest way for somebody not being a cheapskate. Invest a little, save your time.
I am currently doing manual search but it is very very hard. There was a subreddit that would list hundreds of dead subs every week but it died a couple of months back.I don't know of any reliable public list besides r/redditrequest. Most people find inactive subreddits by searching their niche or using Reddit search, then checking whether the moderators are inactive before submitting a request.