Think about running your own Superset instance. Could be the solution and IMO it's much better than Tableau.
Is Superset mature enough? We have been exploring a lot of BI tools so much so that we near scraping the bottom of the barrel. But Caravel/Superset never came up because it is still under incubation and that doesn't go well with the enterprise managers. It doesn't help that there have been constant name changes.
It's great and IMO pretty damn mature. They use it widely in prod at Airbnb so the only ways in which it's not "mature" are in customizability.
What kind of customization?
I think there are just certain scenarios it may not support, like at one point writing queries in the editor for JSONB fields in Postgres was either hard or impossible, things like that. But generally it's pretty great and ready to be used IMO.
What do you use Tableau for? I'm curious we also pay quite a bit but it's a less than ideal solution for us.
[Update: just saw your response to another comment]
What do you use it for?
Making fancy graphs for data analysis. Sorry, I can't get into it much more than that.