Matrix.org is the hugest public Matrix server, plus $100k is not just infrastructure costs, but development and maintenance of the bridges as well. As an etke.cc developer, I can assure you that development, maintenance, and operations even a small bridge is no joke.
t2bot's costs look like infrastructure and operation costs, not development and maintenance.
Disclaimer: I'm Aine of etke.cc, we offer managed Matrix servers with numerous different components, including bridges. Some of the components (like Postmoogle - email bridge) are developed and maintained by our team.
It looks like the site you are referring to quotes pure ISP costs while the matrix foundation bridge costs include maintaining bridge related software they would otherwise archive.
t2bot's costs look like infrastructure and operation costs, not development and maintenance.
Disclaimer: I'm Aine of etke.cc, we offer managed Matrix servers with numerous different components, including bridges. Some of the components (like Postmoogle - email bridge) are developed and maintained by our team.