One of the easiest to build and most cost effective fish structures, is the tire reef.
3 X Used Tires
1 X Bag of Concrete
1 X 10' Length of SYNTHETIC Rope
It doesn't take a genius to figure this one out. Fill one of the used tires with concrete. Place the other two used tires on top of the concrete filled tire to make a triangle shape. Tie the tires together using the SYNTHETIC rope.
This makes a great fish structure that will last season after season, is eco friendly, and will not break the bank.