These don't seem to be inflating so what's cheap?
That bike is on the bucket list of the few who owned them as 1st or 2nd bikes and who also wish they could revisit their youth. No one lusted after them back in the day. Honda made a 400 four, a 500 four, a 550 four, etc in the same time frame. Each may be uncommon, but none are iconic.
Cheap is in the eye of the beholder. Unless you find the guy who considers this his "Rosebud," it will be hard to recover the money in an unknown builder's rebuild.
We sold a handful of them when they were introduced. They're the beautiful, but well known Japanese sewing machine ... modest torque, not much snap, but great as someone's Rosebud. Compared to the CB350 K4 twin, the four was smoother, but more expensive. The few of these we sold were to women wanting to ride with a significant other on a 500+ cc Honda four. In any event, GLWS.
Maybe Barber would like it. I can't remember ever seeing one there. He ought to put together a sequential history of the Japanese invasion and their temporary decimation of the rest of the industry.
He seems more focused on iconic Euro bikes, and in recent years Harley.
Interestingly, I took a docent led tour once, and the docent said that Mr. Barber does not ride motorcycles. He said that the goal was to build a world class motorsports museum. It was too expensive to try to compete on four wheels, but two wheels was almost a blank page as far as world class museums were concerned. He said that Mr. Barber does not ride, even today.