Of course, no business decisions should be made without clear data. How do you know that the time and money spent on accessibility will convert to a return on investment?
If you happen to be among those companies implementing accessibility as the last step of the development process, there is at least one advantage. You can use analytics data to track the number of successful customer journeys (e.g. completed purchases, before implementing accessibility improvements and right after).
Analytics will tell you which stages of the journey saw customer drop off and what changed once the accessibility of that step had been improved. You can also use A/B testing tools to confirm what version of a specific journey is more successful.
Another argument that may convince your CFO to find the budget for accessibility implementation is the risk matrix. Depending on the sector that you are in, the likelihood of being sued for the lack of accessibility measures grows considerably and so do the settlement costs. High risk sectors are those that tend to attract considerable governance measures in other areas, such as finance and pharmaceuticals.
Now add the cost of court settlement, potential reputation loss for the brand, as well as increased engagement in design and development to fix the problem. It simply pays off to budget upfront and become an accessibility leader within your industry, rather than risk the painful process of rebuilding customer trust following costly litigation and embarrassing exposure.