I mean it is expensive, it's just the amount required for a balloon is insignificant and thus seems cheap.
As a diver who uses helium I can tell you it is, compared to air, so much more expensive they actually charge me for it (rather than just rolled into the cost of a dive) - to the sum of about $300 a dive - depending on depth.
The alternative is to use extremely limited quantities of gas crucial for MRIs, chip making, metallurgy, and a few other high tech applications. But hey, pretty balloons.
I mean too much Helium isn’t a problem. It’s one of the few (only?) elements that will just disappear if you don’t do anything with it.
It’s light enough that it rises to the very tip top of the earth’s atmosphere and is then stripped away by solar radiation. That’s why is a depleting natural resource, not because it’s burned or used or anything, but because it just escapes.
The amount of helium produced is truly miniscule, in the order of a few cubic centimeters. They'll just pump it into the ground somewhere, assuming we ever get fusion working