Originally Posted by
corporate-wage-slave
The other factor here is that 2.8k seems a very high sum for the MAN add-on. Now without further details we are in the sphere of speculation, but I suspect that fare came about from repricing an existing booking. If so, then after flying the first leg, it may be possible to change the return sector to start from MAN for a rather more modest fee, subject to the fare conditions.
Indeed. I would question why the agent issuing the ticket didn't offer to use one of the special 'add-on fares' BA files for precisely this kind of itinerary, thus protecting it. This could have worked out more expensive than two separate tickets, but nowhere near the $2.8k mark. Unless I missed something, I suspect OP just needs a better travel agent.