Five of us heading down to Manchester airport on Friday 9th of October.
Did lots of research and testing on this and unless you can get a cheap fare to Wigan with Virgin, at which point you could potentially get a cheap Manchester Metropolitan fare to Manchester Airport, then change at Preston looks like the best option.
Other good option is if you can get a cheap fare to Warrington, airport not that far away by taxi!!!
Used group discount (3 or more travelling -20%) and got 1st Class on Virgin to Preston from Glasgow for £32 each and than booked separately with Transpennine 1st class from Preston to Manchester Airport for £14.50 each.
It also would appear as long as you leave the minimum transfer at Preston, in our case, which is 7 minutes, even if your first train is late, if you get your ticket approved by the first train manager you can travel on a later service than you originally booked for free, only thing you lose would be your guaranteed seat.