help with roaming abroad?

hi im going to spain for a week and im looking at charges for roaming. My phone is locked to orange therefore I need to use an orange sim as I don't want to pay to unlock it. Im currently on pay monthly but I want to use a pay as you go sim whilst im abroad to keep costs down. I've seen a deal which is 10MB for £3 a day which is good enough for what im going to use it for but it says its for pay monthly sims but when I spoke to someone from orange they said I could use it for a pay as you go sim but im not too sure. I cant get any sense out of orange and im very confused at the moment, could anyone advise me? thanks