I use oxypowder, and one bottle has lasted me for a pretty long time.
As the last person said who responded to you, there is the initial 7 day cleanse, but after that I only take a capsule or two whenever I start to feel like I'm getting constipated. So, one bottle for $44 seems pricey at first, but it really will last you for months and months... plus, if you keep an eye on it, oxypowder goes on sale every couple of months.
Here's a link to the oxypowder site, so you can find out more information about Colon Cleansing.