Eleanor - I doubt we're going to agree, although in a sense we already do. I already said I wouldn't want to have one of these "relationships". I personally find the whole thing pretty off. But really that's all you're talking about - personal emotional value judgments about it. Of course we all have the right to react emotionally to various ways of doing things however we do, including being repulsed and choosing not to do them.
At the same time, we live in a pluralistic society where other people will feel differently and make other choices.
The problem with saying this is OK because everyone consents, is that you are saying that hideous old men have the right to fuck beautiful young women who don't want to fuck them, as long as they pay them enough to overcome their repulsion. This is wrong. Nobody has the right to intrude on the body of another human being who doesn't want them there, however much they pay them.
Well really, the old men (I don't think your blanket application of "hideous" to all of them is either helpful or justified by the information in the article) have the "right" to fuck them because they have consented to fuck them. Where such consent exists, and is truly freely given without coercion of any kind, there's no basis for accusing the men of "intruding" on anything.
What you're exploring is the question of why they've consented. We're assuming that in most cases at least, they'll be consenting not because of sexual reasons themselves, but because of something else that they can get in exchange for the sex. You think there's something wrong with this, although you seem to attach all the blame for it to the men rather than the women, and I'm not sure why.
Personally I don't see anything wrong with it (in the sense of "wrong" that is anybody else's business, as opposed to what I simply don't want for myself). It's their bodies and their money, and up to them what they do with them. Your asserting the existence of a "right" about it doesn't make it so.