Not just price, but density is the reason. The next noble gas up is neon, which is quite scarce and more expensive than helium, and denser anyways. After that i

Not just price, but density is the reason. The next noble gas up is neon, which is quite scarce and more expensive than helium, and denser anyways. After that it's argon, which is cheap and plentiful, but about ten times denser, so it's not nearly as good as helium.