A party balloon full of helium is a minuscule amount?
"Let’s say you have an MRI scanner with the OR76 magnet with the full capacity of 1800 litres of helium. Your system consumes approximately 4% of its helium capacity per month, that sums up to 48% per year (4%12 = 48%). That means that 864 litres are consumed per year (1800 litres 48% = 864 litres)."
https://lbnmedical.com/liquid-helium-in-mri-machine/
That is liquid, so for the gas we can multiply 864 by about 1000. So this MRI machine is using 86,000 liters of helium gas per year. That is what, 40,000 party balloons? Say each machine does 1000 scans per year, that is a good-sized cluster of party balloons for every scan. So yes, a single party balloon pales in comparison to the amount of helium being used for MRI scans.
(There are near-zero helium MRI machines, but there are also plenty of older machines in use out there.)
With the most modern generation of reusable space launchers such as SpaceX starship an alternative solution is being worked on, possible thanks to both fuel (methane) and oxidizer (oxygen) they use being cryogenic.
Instead of pressurizing with helium they heat up a bit of the cryogenic liquids using the rocket engine heat, let it expand into gas and use it to pressurize the tanks, no helium required!
One of the reasons is that for fully reusable space launchers the main cost is the propelant and helium in the amounts needed would be a big part of that!
Both are negligible compared to the total cost of space launch currently, but once reusability and operations become more streamlined, they start mattering more.
I know this is napkin math so it doesn't really matter, but a 4% loss times 12 months would be 1-(.96^12) = 39%. Unless of course they're topping up the helium every month.
The other error I now realize is that these HDDs probably have much less helium than any party balloon. They appear to be below atmospheric pressure and are so small that they are probably less than a tenth of a liter each. So one MRI scan is probably the equivalent of hundreds of these HDDs.
For the purpose of worrying about future supply, we probably want to compare to those. A balloon is a tiny waste compared to an MRI that vents helium willy-nilly, but it's a much larger waste compared to an MRI that gives half a care.