. . . but please, please, please, NEVER use Trainline to book tickets! They can't sell you tickets cheaper than you'll get via the National Rail website and you can often end up paying more. Further, I've encountered many problems (in my days working at a railway station) with them issuing tickets which aren't even valid for travel at all!
The journey time is around 1½ hours. There are direct services (roughly hourly) with connecting services (changing at Preston) in between. The 'walk up' fare (which you pay at the station) is £23.00 return. (That's for an off-peak ticket but peak fares don't seem to apply to that route anyway). You might be able to save a few pounds by seeking two single 'advance' fares on the National Rail website but you'd need to remember that such fares are only valid on designated trains. If your flight was delayed you could miss the train that your ticket was valid on and have to pay again.
http://www.nationalrail.co.uk/
National Express also operates direct coach services from Manchester Airport to Blackpool, taking between 2½ and 3 hours (with some additional services available changing at Manchester Coach Station). The fare is usually £6.35 each way:
http://www.nationalexpress.com/home.aspx