Well if we're looking for the absolute cheapest possible spiral-steel corseting corset story
link is a good place to start. There's a section for "waist-training&q uot; corsets, go there - this is the only place on the site where properly boned corsets are sold (flat steel bones hurt!). These things will only alter your shape permanently if you wear them to that purpose; properly fitted, with a waist measurement 3-4 inches less than your natural waist they work just like a regular corset should, sucking in some an keeping it there, but not messing with anything once you take it off.
I have two corsets from that site, and as a reasonably curvy girl (28 inch waist, 40 inch hips, can't tell you anything about boobage though since I'm flat) I can say with some authority I think you'll love the way a proper corset will make you look ^_^. That being said, also from the standpoint of someone who's curves are of the pelvis-y persuasion I feel I should warn you that you'll want to break in the corset carefully if you have anything like hips, otherwise the fight between the boning and your hip-bones can result in really uncomfy rubs and bruises. Wear it only for 1-2 hours at a time at first, laced tightly but comfortably, as straight up and down as you can make it. Over time the canvas over your bony areas (hips and rib-cage) will stretch to accomadate your shape and the waist can be cinched down a little more, affording you greater comfort in the garment and a prettier over-all shape.
If all that sounds tedious, and you're willing to spend a bit of extra cash (and wait for shipping from GB), Axfords has absolutely delicious corsets, all with spiral steel boning, that are made with varying sizes in the bust, waist, and hips, so they come already fitting like a glove, not to mention some of the absolute best customer service I've ever run across in a lingerie store. I can't recommend them enough (
link) but they may be a bit steep for someone that is not sure she will like this type of garment yet.
These two links, and a couple other corseting sites are all listed under my public profile's favorite websites, if they do not work here for whatever reason.
I hope that helped, and please excuse the wall-o-text, corsets are kind of a passion for me ^_^;