Helium has gone up a lot lately. You can do cheap balloon grade stuff for about $75/300cf, but once it’s under pressure, it doesn’t float any more, so there is almost no weight savings. You can run some combined gas calculator to figure the difference in moles between air and Helium.
We used compressed Nitrogen in aircraft tires, but mostly because they’re inflated to between 250 and 350psi in most cases and the N2 is more stable at various altitudes since wheel wells are not pressurized.
Honestly, both would be useless in a bicycle tire other than the placebo effect perceived by the rider. Air in 79% N2 anyway. You could also run your air through a dryer before compressing it.