Not too long ago, I wrote about suspended training. There are a lot of good suspension training systems out there, most notably Blast Straps, TRX, or Gymnastic Rings. The problem with all of these is they're all pretty expensive, often times running up to $100. Now, for the sheer variety of exercises that you can do on them, I think that they're worth the investment.
However, some of us just can't part with that kind of money (or don't want to... us cheap bastards!). Part of the reason I started this blog was because I wanted to have a site that shared ways to do strength training on the cheap. So, I felt I'd be doing a disservice to my readers if I couldn't provide a far-less expensive alternative than TRX. Fortunately, this kind of equipment is very, VERY easy to improvise for a tiny amount of money. All you need, is some rope, a couple of 3/4" x 4-5" nipple, a length (or two, depending on your set-up) of rope (around 3/8- 7/16", the rope should be able to hold at least twice your body weight), and some knot-tying know-how.
Make the handles in the rope by using a Bowline , putting the plastic nipple in the loop. If you want, you can make this Bowline stronger by adding second crossing turn. On this particular piece, I am using only one rope. It's set up to hang over an open set of stairs at my hotel. You could use a similar set-up for a pull-up bar. To secure it to your bar, you might want to use a cow hitch.
If you want to raise up the handles, so you can do dips or rows, then you can shorten the rope by using a sheepshank. The top one will suffice. The Man o' War Sheepshank is a really attractive and strong version of this knot but you probably won't have enough rope to tie it effectively. What's really important when tying the sheepshank is to make sure all of the crossing turns are going in the same direction. If they're not, it'll come undone under a load... and you'll come crashing down to the ground.
The one piece version that I made up is simpler to make and is easier to use. If you want to make the exercises harder, you'll want to use two independent ropes. That's very similar to what I have in my basement at home. For that, I put a few hooks through the beams in my ceiling. I put several. Increasing the distance of the two hooks apart makes the exercise harder. Then, I simply tied a second set of bowlines on each rope and hooked them on the hooks in the ceiling. If you wanted to tie this set-up to a tree, then I might try using a timber hitch. The advantage of a timber hitch is that it's easy to untie, doesn't slip very easily and the more tension put on it, the harder it grips.
Overall, you could build something like this for a measly $8.00. I also recommend that you practice tying each of the knots that I referenced until you're proficient tying them. I know that this rig is not as sexy as any of the pro-suspension trainers but it also costs about a tenth of what they're currently running. Plus, it goes to show that you don't need to spend a lot of money to get a lot of results.