The lack of subscription and signup, combined with the pricing, suggest that this is aiming at people who almost never send a fax, and would spend significantly more buying and maintaining a fax machine, compared to a couple dollars on this service.

I do hope you find a service that fits your need, but this is very likely not intending to be it.

Right, but is it a viable business if the average customer spends $1-2/year or less?

A business phone line ($100/month or less -- crap tier VOIP lines work fine for faxes) and a PCI fax/modem (<$50) should let you send hundreds of pages an hour with no paper or other consumables. It certainly seems like a send-only service that charges $0.01/page is more than viable. Even averaging only a page a minute would be $15/day in revenue, a huge profit margin.

If they have enough customers, then yes.

Who the hell wants to buy a fax machine?

I don’t care how much you can buy one for, I’d pay a premium to not have to have one or set it up.

You're forgetting the cost of a landline each month.

Every business already has a phone line or ten. Plugging in a fax machine for 90 seconds a week is not a major hassle.