Helium is released from alpha decay (hence unlikely to run out in the near future) and is also obtainable from natural gas. That being said it is still non-renewable (in the sense that once the radioactive decays happen no more helium is released) and has quite volatile prices for some reason.

Helium might be expensive, but there is some orher lifting gas that is not. Water vapor. It has about half the buoyancy of helium. It is a bit more complex to use it, because you need to a way to collect the condensation and boil it and send the vapor back. So helium can be used to kickstart the airship production, and once we are reasonably good at it, we can switch to water.