Does it matter? Tomorrow morning you can wake up needing those accessibility features.
Accessibility is valuable but not infinitely so. Sometimes (usually) it’s best not to encumber an innovation just because the innovation doesn’t immediately apply to everyone.
They asked "what does it cost vs just ignoring it". The point is just ignoring it (in other words assigning it 0 value) shouldn't be on the table.
I'm also giving this person the benefit of the doubt and assuming they're not asking if accessibility costs infinity dollars.
For a lot of things a18y features are just good features in general; zooming text for example is something loads of people do, not just blind or low-vision people.
Need to define it at least a little to get anything resembling a useful answer.