bjkTX , The invitation to bid is for an upgrade to one of four classes of cabins, upgrade to { obstructed balcony(starts at 100/99, obstructed delux balcony(starts at $150/pp), standard balcony(starts at $200/pp), and deluxe balcony(starts at $250/pp)}. I had an inside cabin far aft. I was upgraded to a deluxe obstructed balcony for $100/pp, occupancy 2, far forward.
You have to agree to accept the new cabin immediately, no problem, I just booked the cruise, I didn't have a great location before, now have an OK location at the other end of the ship. I'm happy.