How expensive are flat irons?

I am thinking about starting to straighten my hair to get a bit of a different look every now and then. My hair dresser has mentioned that my hairstyle would also look good if I straightened it, so I am thinking that it would be nice to give it a try. I would need to get one of those flat irons though in order to do this. Are they very expensive? I seem to remember seeing some that weren’t too bad. Are the inexpensive flat irons just as good as the more expensive ones? Or is there something about those that make them better?