I can highly recommend Dr Schulze's Intestinal formula #1 and #2 (his bowel detox), especially for the most constipated people. His formulae really work well.
To cut on costs, you can buy Intestinal formula #1, and instead of #2 buy (bulk) psyllium husks, flax seed (whole, which you can grind in a coffee grinder or food processor) and fine bentonite/green clay for internal use. Use flax and psyllium 1:1 (50/50). Look up 'P&B shake' here on Curezone, or with google, and you'll find how to make a bowel cleansing 'shake' of psyllium (and flax) and Bentonite clay.
I also recommend to buy Dr Schulze's booklet 'Healing Colon Disease Naturally', which teaches you basically all you need to know about colon cleansing, and how to a bowel detox (using Schulze's Intestinal formulae #1 and #2). Fore more info and products, see: http://www.dr-schulze.com. There are also a few other sellers that sell Dr. Schulze 's products and books, but you'll have to search for them online.