Tweetpsyillum husks - take a level teaspoon with each meal or as fits your tolerance. It really makes the diet more bearable.
Assuming you are not allergic to them, the husks are the cheapest way to go. Make sure you get type that is sweetener free. You can also get them in capsules for when you are away from home and don't feel like popping open a can of colon blow around your friends.
Jorta