But you need to be aware that then those folks coming into the org with a non-org domain email address are Guests, not Members, of the org. See my recent reply on this topic, and the link to the Asana Guide on Members and Guests:
It’s not as frictionless as paying for all, but perhaps the only affordable option for some.
Are you able to qualify for the TechSoup discount? Or perhaps @Michael_A can help?