If you're trying to get closer, macro extension rings are often the better option over bellows these days. The variability of bellows was important in the film days with primes, when getting the subject to fill the negative was all-important. A zoom lens and three extension rings will give you the same degree of adjustment, but in all but the super-cheap versions they'll also pass the electrical contacts through. Even when you're shooting manual it's handy to get the right EXIF data on file.
Going the other way, pairing teleconverters with a macro setup will increase the subject distance but you'll take a big hit on exposure. You can go to town and put TCs and extension tubes together on a 200mm telephoto, and you'll be snapping flies from 6ft away. Probably need a tripod for that though
So you're saying that using extension tubes will not only increase the focus distance, but the magnification/focal length as well? If that's true, then lets say I'm at 80mm on my lens. How many sized ones would i need to get to 150mm?