I saw an instructable for a TRX under $25 that suggested It could be made of paracord, I took that as challenge and made seven of them, for Christmas gifts. Each was under $9. So, to start you'll need to gather three materials: Paracord, Handles, and Carabiners.
Step 1: Knots of Fun
Step 2: Lark's Head or Cow Hitch
Use this to make the connection between a 6'0" piece of Paracord and the middle top caribiner.
Step 3: Constrictor Knot
This knot gets tighter, as the name suggests. Use this knot to tie one carabiner to each end of the 6' para cord. This completes the top center piece.
Step 4: Rolling Hitch
Cut two pieces of para cord such that they are long enough when doubled they will fit the hypotenuse ' c' in a triangle a,b,c, where a=9', b=your height (to the closest foot) its own carabiner at the end of the top center piece. Create a loop by tying a rolling hitch.
Step 5: Bowline
tie the handle on with a bowline.
Step 6: Resources