Because prices are plummeting (and the current situation re Coronavirus) I phoned my TA yesterday and asked for a price to upgrade from an inside cabin to a balcony. I was quoted in excess of £900 although a balcony cabin now costs what I paid for an inside. I was prepared for a few hundred more but not that much! I am due to sail in April so have paid the final balance. She was adamant and said I should wait and see if I could pay for an upgrade after boarding. Has anyone been successful doing that?