Building from scratch probably won't save you any money over building an FFR kit. By time you acquire all the material, figure out how it all goes together, then buy all the instruments, wiring, drivetrain, wheels, etc..... you'll be into it more than you can imagine. Don't ask me how I know this......
Your best bet if you want to save money is to keep your eyes open on the ffcobra.com classified ads and craigslist. Their kits come up unfinished for varioius reasons on a fairly regular basis and sometimes the deals are pretty great...
Bob