There are already two feature requests to provide integrated TOTP authenticator functionality in the Free ($0) plan:
And as @DenBesten mentioned, the regular Premium plan is only $10/year.
So, would you like to propose a new plan that is more than $0 but less than $10 per year (and includes TOTP but no other Premium features) — if so, what would you propose as a price?
Alternatively, if you wish, I can move your post into the existing feature request for free TOTP.