I agree with everything that Matt says here. Evangelising accessibility by extolling the business benefits might be a good strategy for dealing with psychopaths, but it’s a lousy way to convince most humans.
The moment you frame the case for any kind of inclusion or equity around the money an organization stands to gain (or save), you have already lost. What you have done is turn a moral case, one where you have the high ground, into an economic one, where, unless you have an MBA in your pocket, you are hopelessly out of your depth.
If you win a business-case argument, the users you wanted to benefit are no longer your north star. It’s money.