hi Raglan2;
Yes you sure can check in at the airport. There is no cost for that! The only thing is you will need to Queue up!! You can buy speedy boarding at the airport, not sure of the price though. I saw at my local airport this week that Easyjet have a sign at the gate saying 'to purchase speedy boarding for this flight, contact staff at the gate', so presumably you can buy speedy boarding just before the flight is called.
Have a good trip!
EI-BUD