Cheapest way from Hull, uk to Belfast?

Hi, I need to get to Belfast from Hull the cheapest way possible. The journey will include getting to the airport somehow, then flights etc. I have 2 children aged 7 and 4 and obvioulsy Im an adult. Lets see who can help me and find me the cheapest possible journey for 17th October 2008 - 20th October 2008! Thank you x