Suitcases are an important part of any wardrobe. What do you need them for? Why not use a plastic trash bag? That will work in a pinch, but when you use one of those, your clothes get wrinkled!
I have two suitcases, one for light packing and travel, and the other for longer trips. Its good to think about the size of smaller suitcase, because if they are small enough, they can fit inside the overhead compartment of planes, and thus be used as carry-on luggage.
Suitcases don’t have to cost you an arm and a leg. I bought my luggage at Filene’s Basement to save a few dollars, and its actually quite nice. Shop around, I’m sure you’ll find some decent deals. While I’m sure others have had different experiences, I had a poor experience with e-bags.com. I can’t even remember what went wrong, but I do remember deciding not to purchase from them again.