I made this monopod from $10 worth of parts available at the local hardware store (5' broomstick, 3 T-nuts, 3 metal dowels, 3 carriage bolts (cut heads off), 3/4" Sched 40 PVC parts - T-connector, Elbow, 1" Coupler, and two short pieces of pipe, one being a thin-walled 1" piece.
As you can see, it has an unbrella holder that I use it for shooting soccer action on rainy days, or it can be removed and fits in my camera bag. You can built it cheaper and simpler if you don't want to be able to unscrew it to reduce the length, but this is handy for storage and to create a second shorter monopod for use while sitting. If you only want a fair-weather standing model, then you can make it for about $5. Tools I used include: Hacksaw, Drill & various drill bits, metal file (to smooth cut ends of threaded bolt), miter box & saw, hammer, screwdriver, plyers, 1/2" brads (tiny finishing nails), PVC cement. PVC parts can be found in the plumbing section of the store and other hardware where they keep special fasteners or furniture parts.
Update: See the last 4 photos. With a slight modification, the umbrella holder works fine on a commercial monopod! Now that I have a larger and more expensive DSLR camera (Canon 10D replaced the Pro 90), I did not want to trust my investment sitting on the small area atop a wooden brookstick which I was afraid might break one day under the increased weight of a long heavy telephoto lens (Sigma 100-300 f/4), so I bought a commercial monopod and adapted the PVC parts to snap onto it. Bogen/Manfrotto models 3249/680B Monopod (about $50 from www.bhphotovideo.com, B&H catalog # BO680B).
