Hi Sarah
As Mark rightly points out, its all about timing and dates, school holidays, bank holidays will always be the most expensive.If I lived in Blackpool the last possible place I would want to fly from would be Gatwick, it would take at least 5 hrs by coach add the 2hr check in time, the time to meet and board the coach, and you will probably be leaving your home the day before you fly.
If you want to come out in March 2010 check airline websites for spring/summer flights as they come available, around Sept/Oct this year.
We have had some great prices this year from Monarch from Luton to Malaga, we are out again 10th May and paid £89 ea all in, these flights were booked in February.
I would also suggest you might try Birmingham, East Midlands or Coventry.