My understanding of this is that there's different qualities and mixtures of helium. When you buy helium from a party store it's a kind of "dirty" helium which is not pure enough for scientific/industrial applications.
The regular helium grade purchased from industrial gas suppliers and typically used for filling party balloons is >99% pure. There are higher grades available for specialized purposes, but using lower grades doesn't save any helium.
https://zephyrsolutions.com/what-are-the-different-grades-of...