Edit: The cheapest ARM processor I found on Digikey is $0.35, Digikey must be buying them for under $0.15 so that royalties would be under 3/10ths of a cent.
It is simply way, waaay too expensive to operate a fab nowadays.
However it's so insanely expensive to set up that type of chip manufacture the only way it is really viable now is to share the costs. Samsung, TSMC and Intel (and maybe GF) are the only groups left who can afford it (see http://www.eetimes.com/document.asp?doc_id=1327060 ) and you have to keep up the r+d every year to stay competitive...
If you make other people's chips on the same fab then the per chip costs go down, assuming there is spare capacity. The economies of scale really do help. Which is why there are a few foundries who do most of the chips, and those foundries can spread the costs over a large number of chips including later ones that don't need the newest process. For example Intel is known to do their CPUs on the current process, while doing the chipsets on the older processes.
In other words, work out what set of numbers would make sense, and you won't be able to find any. New processes keep getting more expensive, and competitors adopt them too, so you have to sustain your current fab as well as the work to do the next generation one. This requires a lot of available money.
Don't build a fab unless you are sure you can use almost all its capacity for the next several years.
Getting a new, smaller process to run well is expensive and difficult, but gives important benefits. If you don't run your own fabs, you can't jump ahead of others.
But you are also safe from investing a billion or a few in an upgrade and it not working out properly, and you still can get basically the same tech as all the other fabless companies.
STM, NXP, Mediatek, etc buy the core design, slap it on a piece of silicon, design peripherals around it (SATA ports, UARTS, SDIO controllers, etc), slap those on the silicon, put interconnects in between, and sell the complete SoC.
This is of course EXTREMELY oversimplified. But the idea is the same: ARM makes the CORE, and others make SoCs out of it. (I am not aware of anyplace you can buy a simple ARM CORE without it being part of an SOC.
acorn one was 'Element 14 Ltd', purchased by Broadcom, now Avago.