For one, they haven't made it clear that they need to take them down; they said they are going to do whatever they can first, but leave open the possibility that they will be unable to meet the regulations and would need to remove the content.

I understand your argument, but if you only have to say "I can't afford to support disabled people!" in order to not have to be in compliance with the ADA, then the ADA becomes meaningless.

The answer of "we can't afford it" is always about priorities. They could choose to spend money spent on other things to make this content accessible; it isn't like they are spending their entire school budget on this. It is ALWAYS going to be cheaper to NOT provide accessible content, so this argument could happen in every single instance. The resources spent making content accessible could always be spent on making more stuff for non-disabled access. However, as a society we have decided, no, it is unfair to choose not to spend those resources on accessibility,so we mandate it, because we know a pure utilitarian action will leave disabled people always getting the short end of the stick.

Yes, this means that non-disabled people will lose out on some stuff (and maybe this content is one of those things). That is a price we as a society have decided to pay, and I think it is a worthy one.

Think about it; the same goes for handicapped ramps and the like. If businesses didn't need to pay for those, they could use the money on other stuff. Prices would go down. So yes, we all have to pay a little more so everyone can enjoy the same access (or at least a certain level of access)