I guess it depends on where you fly. The routes I fly to Europe and South America are typically 5-7K although I have seen less. It also depends on what type of business class seat you want. If you are fine with the older style reclining business class seat you cloud fly Copa for $3500 or even less sometimes. If you want a modern lie-flat product like Delta One or United Polaris than you are going to pay a bit more. I typically can book in advance though.
Depends. I’ve gotten business for as cheap as $2k one way transpacific. Got lucky once and scored ~$900 between Beijing and Bali round trip. Google flights helps a lot if you have flexibility.
Flights in Asia are generally far cheaper and, in my experience, more comfortable. Business class on longer flights in Asia is much cheaper than the same distance in other places I visit. But usually economy has less seats / more space too, at least in the airlines I fly with.