I;ve never done the airport bit, but have got great value last minute via internet... budget travel / mytravel.com (out of Belfast) are 2 that have worked for me on a number of occasions.
If anyone is really looking for last minute deal I spotted 1 week in Orlando leaving from Manchester tomorrow for £44.... of course by the time they add in car insurance, fuel surcharge, meal on flight (you can opt out if you want), it was more like £200.... and thats before you even fly over!