I mean, I don't think that's a good argument - it costs you cents per user. Either way, I think you should charge however much value users can take from the product, completely unrelated to the cost.
At the moment though, being notified whenever my github repo is trending is a nice to have that gives me nearly 0 value as there's no actions I can take from that (other than share with my team :)). So I would try to find some other way to monetize it or to bring value to the users. Sorry for the harsh feedback.
Not at all harsh! Very valuable. Tbh it was really about just trying it out for now, its very arbitrary! :-) Do you have any suggestions on what exactly you'd like to do after you find out its Trending?