Way, way less. International F/J fares are inflated, because airlines know most of the paid seats go to people who are not price-sensitive: business travelers spending the money of anonymous stockholders or wealthy individuals to whom either $1,000 or $10,000 is petty cash. Many of the seats in any premium cabin, though, are occupied by people who redeem miles for tickets or upgrades. Others go at very deep discounts to companies with corporate travel arrangements with the airline, deals such as the AmEx Platinum* two-for-one offer, and so on. The airline revenue from either cabin isn't even close to what you'd get by multiplying the fare by the number of butts in seats.

I suspect the transfer price for a seat among partners is close to our perceived value of the miles needed for the award.
_____________________________
*Only real AmEx Platinum. Not to be confused with platinum-colored AmEx affinity cards such as those branded for Delta, Hilton, etc.