Hi carly,
I would definately recommend the Avent cups too.... the coffee cups might be cheaper but you cant be sure there arent any nasties from the styrofoam that might get into the food....
I know its hard when your looking for a cheaper option.... but with those Avent ones you can micro wave them, stick them in hot water and they are always reliable to stay air tight when they are in the nappy bag..... and they are reuseable too
good luck and enjoy your trip overseas lucky duck :P