Well I have experience with wearing corsets, but getting one that's affordable depends on where you live. I know a woman who does wholesale corset orders and they're generally very affordable, and if you think it's an option I could pick it up from her and ship it to you. You would have to wait for the wholesale order to come in though, so that would depend on when you need it. If you think that might be an option I can pm you with the login for the wholesale site and you can look at the catalog and stuff.
With corsets you want to order them smaller than your waist size if you want to get a "corseted" affect. If you're new to corsets I recommend getting one 2" smaller, though if your waist size is an odd number I would go with three rather than one (the corsets are only even sizes) When wearing it, be sure to loosen the ties enough that you can get it around you comfortably, then make sure all the hooks are closed before you start to pull the strings from the center of the back.
A properly laced corset is always pulled from the center, and not the bottom or top. You'll have to adjust as you tighten it so that it sits properly and your bust doesn't get squished and all that. You can find lots of tutorials online on how to properly tighten your corset but there's a good one here.
One thing that I've learned that's kind of cool is to hook the strings around a doorknob, then close the door while you stand on the other side. You can walk away from the door and it will pull the strings for you! Also, a corset will force you to have good posture, but it should never restrict your breathing. If you feel very uncomfortable (it's a corset, you'll probably feel a little uncomfortable no matter what) then take it off right away. Be sure to loosen the strings before you try to unbuckle it or you can damage it.
Also, the boning will eventually bend to your body shape and become more comfortable over time, so never
lend your corset to someone else. Their body will bend the boning and it won't fit you as well.