Why Do 12" Tonearms Cost So Much More Than 9"?

I think they are somewhat less. I have a relationship abroad who say I can get one for $10,000 (wink wink). I'll have to pay VAT tax up front but I'll get it back in several months.
The dealer in the States is Xact Audio  https://www.xactaudio.com/analog/
He sells it with or without his own turntable but he modifies the arm replacing the wood for a magnesium arm tube which I am really not crazy about.  He has some kind of relationship with Schroder apparently he can sell them here in Magnesium and Frank can sell them in Europe with wood. As for his turntable there is too much mystery about it for me to be sure. I think if I could afford to today I would get a Dohmann Helix 2 and put an LT on it. That would certainly be a last stop turntable.
Not to worry Uberwaltz. This type of design will work it's way down market. Reed is working on a less expensive version now called the 5A.
It is another passive design energized by groove friction but it uses a dizzying series of arms and bearings to do the job. The Schroder is certainly a more elegant design. You have to love the magnetic track trick. One magnet + one bearing vs a bunch of arms and bearings.
The 5T is however a beautiful arm and boy does it work. It is $20K and very complicated but still a grand exercise of applied technology. 

And Uberwaltz, Franks other arm are also genius. Check out the CB. You can get one for $5000 and it could easily run for best pivotal tonearm made. 

lewm

my first thread here was asking about long arms

https://forum.audiogon.com/discussions/tt-12-tonearm-who-tried-and-ended-up-preferring-12-arm-2

then I asked specifically about the Blackbird 12.5

https://forum.audiogon.com/discussions/12-1-2-arm-newartvinyl-black-bird-yea-or-nay

and about the 9" arm I found

https://forum.audiogon.com/discussions/tonearm-acos-lustre-gst-801-yea-nay
.......................................
chakster was involved,

as I said, no one said 'good idea', chakster said NO, the only thing they make in Russia is military weapons. That definitely slowed me down. Next, Vlad, the Russian in Canada that sold me and Bill our large JVC Plinths, said he never recommends anything he is not personally familiar with. 

Months, nothing else excited me, finally I had to risk it. I discussed the specifics with Square Trade before I bought it and their 3 year warranty.

Those tiny wires were quite a trial, now quite an accomplishment. If they would pre-wire to a din or mini-din connector, they would sell a lot more of them. Stubborn, they say they tried several, but like the sound without a din connector. 

I love this arm, very glad I risked it.

the real deal

https://www.artisanfidelity.com/tonearms/ikeda-it-407

Thank you Mijo again.

The CB also looks very interesting especially in the CB-L version.
I also see there is a collaboration between Frank and Peter at Soundsmith to produce an arm called the Alto at $6k although information seems to be a little sketchy on that?