Are you returning to the airport to get the transport? We got a coach from a central London hotel. Doubletree West End I think it was. If you actually need to go back to the airport, that about 80-90 GBP by taxi plus you have the charge for the Disney transport. (Elizabeth line is of course cheaper, but this couple in their 60s and me recovering from knee surgery weren’t doing that.). Might be easier and only a little more to take taxi to Southampton.