The good news is that the Bentonite and psyllium are CHEAP. I have a big bottle of Bentonite (about a litre?) that I bought for about ten dollars. The psyllium is great on the budget as well. I picked up a HUGE jar of it for about twelve dollars Canadian. The Bentonite has lasted about two months.
Have you actually been diagnosed with IBS? A doctor will probably want to run some tests. I had to do a barium enema (ugh) to rule out some more serious possibilities, but afterwards it was worth it :) Have you had any sort of testing done?
There are several things that give similar syptoms to IBS like Chrohns. I would not take ANY medication until I had a diagnosis from your doctor, and then only in those "emergency" times, if possible.
If you do the B&P cleanse (as it is called!) make sure you take some good pro-biotics to replenish the "good" bacteria in you.
(The clay and psyllium will draw out good and bad bacteria so you want to make sure the good stuff goes back in!)