You can upgrade your browser but you can't upgrade to a body that isn't disabled (yet)

I agree. But I mean it in the sense that they are a very low % of users and you have to ponder if it makes sense to spend the money to support them.

Using semantic html like nav, list, header and so forth is basically free.

that would be discrimination. your country likely has laws to deal with this.

The basics of using the semantic tags are easy enough that I'd question if that counts as "spending money" in any relevant amount.