I've arranged a euro-trip with some friends of mine, and we just finished completing the task of booking our airfare to, and within, europe. Within europe, most of our flights are with budget airlines. Originally, I was planning on just backpacking it, and using my bag as a carry-on, so I didn't purchase the option to check-in 1 piece of luggage. Looking a bit closer at the dimensions for carry-ons, it might be a bit tight, and I'm thinking of maybe wanting to check-in a piece of luggage now. Before I start calling the various airlines, from your experience, do they typically let you purchase that option at the regular price if you call them in advance (so I don't get dinged at the airport and get charged a huge fee)? Thanks!