Low cost airline prices are not all they are cracked up to be.
You have to fly when they want you to fly to get the cheapest fares,In some cases this may be totally inconvenient to you or your travel plans.
I used to use GO to LIS, then found out BA was cheaper!.
LHR is only 20 minutes from my house so what can I say.
Basic rule,shop around,don't travel on school holidays if you can help it.