Hey. New to this RX7 Forum stuff.

I'm from the Bay Area, CA & I have a 1990 Mazda RX7 Convertible Non-Turbo Manual.
The transmissions going out, and I decided to just try and find a new one & have that installed.

Would anybody happen to know any good places to research for good used transmissions?
And/or would anyone know how much a job like that would cost?

Thanks!
J