The biggest question: "What foods have fiber?" Predominately, you will need to look for whole foods, especially in form of plants, vegetables, fruits, nuts, and grains.
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(Apples and strawberries contain soluble fiber.....and are delicious!!)
Here's an article from Health that lists 20 great sources of fiber and also has links to recipes to help you figure out ways to include more fiber in your diet.
http://www.health.com/health/gallery/0,,20553010,00.html
And here is another with lists of fiber-rich foods:
http://www.webmd.com/food-recipes/features/fiber-how-much-do-you-need
The good news? A lot of these foods are easy to find at your grocery store, and can be bought on the cheap, so you don't have to worry about being healthy while going broke at the same time!
ENJOY!