In the best (and thankfully pretty common) cases the work to do the accessible answer can be the same, or even less, than the work to do it otherwise. That certainly doesn't extend to all cases though and that's where it can snag. E.g. making complex charts or visualizations accessible to those using screen readers often involves creating a second version of the information only suited for that modality. A ton of other things are a bit in-between, such as prefers-reduced-motion being somewhere between "pretty easy" to "complex" depending on how you implement it in your site but, either case, adding some amount of effort.