At $199, the TRX Suspension Trainer is cheaper than most gym equipment. Its body weight resistance exercises are challenging enough for elite athletes yet can be regressed to suit even the most deconditioned individuals (See examples at the TRX, ACE, or BodyLev libraries).
There are tons of TRX clone instructions but this design is uniquely inexpensive, strong, and easy to make and use. I've included simple instructions for an attachment that makes hanging the device a breeze, even for anchor points higher than 9 feet.
1) Two .5" by 4" PVC pipes or sprinkler risers (pre-cut PVC pipe for sprinkler systems) - $0.56 each
2) Two 8' x 1" Lashing straps with cambuckles - sold together for 7.97
3) One 15' or longer x 1" lashing strap - $3.47
5) Tennis Ball (Optional - see last step)
6) Clip / Carabiner (Optional - see last step)
Total Cost: $12.56