I don’t know whats the direction internally nowadays, but unless Discourse team has tooling for Telligent, they won’t be able to migrate for you under business. Onboarding a new platform on their tooling used to require at least enterprise.
I’d send a message to the team, they are really nice people and will help you understand more about the migration. You don’t need to sign in advance to get a quote.
If the team doesn’t have the tooling, we have many community members available to work for you as a consultant and perform your migration while still signing the business plan.