Buy old tools!
Flea markets, secondhand stores, and craigslist are some of the best places to start building up a set of basic tools for your parkour construction projects.
Keep an eye out for "vintage" well-built handtools and simple power tools. We get a lot of our equipment (and grab bars) from a fantastic secondhand place called the Restore in Seattle. I spend hours there picking out old, heavy, well-used stuff, even if it's rusted or slightly dented. I figure if a tool has lasted a long time already and still works, it will handle anything our well-intentioned volunteers mis-use it for ;)
The best part of picking up old tools that require some de-rusting or fixing up is the learning experience. You'll learn how simple machines are put together and how to care for and fix your tools.
You'll often end up with something awesome that only cost you some WD-40 and scrubbing. An example would be this old vise I picked up for $5. Every moving part was severly rusted shut. Eric teased me about picking up a complicated doorstop, but it cleaned up reasonably well and works!
