Sharon,
My Canadian cell has 5GB of data in Canada but roaming cost me something like $5-6/MB for US and an outrageous $23-26 when I was in Europe. To prevent any surprises, I simply turn my data off. I text if I need to and even though it is .75 sending and receiving for my phone internationally, it is better than getting surprised with data.
I monitor my data usage and things you don't expect take data. Like GPS finding your location, Skype login automatically with data, sometimes my yahoo or gmail get mail automatically since I have the setting for my PC and if I log ino goggle talk or yahoo im, sometimes with my android phone some apps get hit by mistake and it goes to my book marketplace app, etc. all those take data and even with minimal usage on web, sometimes I get 500MB in short order.
I think T-mobile used ot have an international plan for $30 and I know some people who used to travel to Europe who used to be on it. But with the advant of smartphones, they no longer sells it.