Combine an old BMX bicycle, wood, EMT conduit, and boat seat, to bicycle in laid-back comfort. Save $100's off the cost of a new recumbent bike.
Step 1: Use wood for a main beam across the top of the BMX bike frame. Wood is easy to work with, but does flex a little when you peddle.
Step 2: Attach boat seat, bottom bracket with peddles and chain guide-wheels (2) to the main beam.
Step 3: Note front wheel drive. Use a rear wheel in the front and a derailer to keep the chain tensioned. Chain will flex enough to allow normal steering.
Step 4: Use EMT conduit to raise the handle bars enough to avoid contact with your knees when you peddle. Handle bars must be very rigidly attached to the front wheel. Any looseness will make steering difficult.