Be aware I tend to price low. I would be higher in pairs than for all 4. After all, you have to do two transactions to get your money.
Even at that, I would still be reluctant to break up the 4. There is a customer who wants all 4.

I would want $1600 for the 4. If you check what GPA would want, that's dirt cheap. And where but you or Great Plains are they going to find 4?

I might start out higher and offer to ship to Japan. Have them professionally foam in place packed and charge the customer, likely 50 bucks each.