If you can find Silver Hills brand, Squirrelly bread (yes, squirrelly as in the woodland critter) is my ultimate favorite. Has a rich nutty taste to it that I absolutely love despite not actually containing nuts. Has approximately 20% of your daily value of fiber per slice.
However, as far as healthy and cheap goes, Kroger sells a Private Selection bread called Flax and Fiber that tastes decent and also has 20% of your daily value of fiber per slice. It is almost always on sale for $1.88 so it's definitely the best bang for your buck.