How is MapBox going for this free tool? Is it costing you money?

It definitely will if it blows up more. I'm willing to eat it for now because I think it's art that more people should see!

Is MapLibre GL a cheaper (free?) open source alternative?

Cool stuff btw. I’m trying to visualize weather model data myself (millions of points) at https://futureradar.net and have been researching client-side techniques like yours.

It is very cool art!