From my experience it shouldn't be nearly $2,000 for you especially if you just want to go to a concierge stateroom v. a 1BR or Royal. Of course it will depend on the price of the rooms when you booked.. but given the cost of your 5C , I am guessing you are on the higher end of the spectrum. We have paid as little as $400 (for 2A, 1C) for a concierge stateroom upgrade from an 8A and as much as $900 for a 1BR from a 11A.
My upcoming cruise is a 14 day Panama Canal cruise. It has already been heavily discounted from the opening price. $8000 for a verandah is as low as you can go (I actually had a 25% discount certificate and booked on board for another 10% off. I actually paid $5700 but I didn't want to confuse the issue). If I can get an upgrade for under $2000 I think it would be a great deal. (but maybe some of the concierge guests would be upset at me).
They also sole IGTs on this cruise, would have been $4600 for all 4.