This was mentioned in another thread at some point in the last few days. LAX-SJU seemed to offer the lowest fares I could find, but I think there were other Caribbean cities with similar or slightly higher fares.
It smells to me like a complete oversight by revenue management. There's no way they should be permitting access to the AFS F cabin for $600 one-way, particularly when that only covers about 60% of the total trip mileage.
Worth noting, you can buy this as a one-way fare ex-LAX...