I agree with the above poster that the prices for Spanx are pretty consistent. I would warn against using an imitator. For example, once I tried some shapewear from
Walmart, and let me just say it is not all created equal !
I thought I was going to have a heart attack when I bought the one that is a sleeveless slip (basically a tube shape) and it cost $98. But it was for my wedding, and it was worth every single dollar. I use it all the time under dresses, and even under skirts and blouses. I also purchased a pair that look like underwear that have legs to the knees and that come up under the chest. Those, I believe, were in the high $30.
It's worth every single dollar I've ever spent. The products are sturdy. Other kinds I've tried have fallen apart after a few months, but these are going strong at over a year and a half. Even if you're a smaller woman, they're great. I have a friend that's a size 2-ish, and I rolled my eyes at her, but she showed me the difference before and after, and it really blew me away.
I'm starting to sound like a Spanx rep now, but I just wanted to let you know that they're one of the best products I've purchased in a long time and worth the investment !
As for retailers--larger "flagship" stores in malls should carry them. Lane Bryant also carries them but, of course, only carries larger sizes.
Best of luck !