Want to see what everyone is talking about with this whole 'Single speed revolution?' Before you commit several hundred dollars to a single speed bike, try it out on your current bike without costing you a dime. All you need are basic bike tools to get it done.
Step 1: Choosing a Bike
Since the aim of this project is cheapness, use a bike you have laying around. Many bikes will work for this, as long as it has one crucial component, a horizontal ( or horizontal-ish) dropout. While it is possible to convert a bike with any dropout to single speed, it takes either a great deal of time or money, neither of which are appropriate for testing the waters of single-speed bikes.
Other things to look for:
If the bike has horizontal dropouts, it will work, but if you have the choice, get a frame without brazed on cable stays. They will only affect how your bike looks, but appearance does count sometimes, and single speeds look cool, so why mess with it.
Step 2: Break the chain
Use your chain tool of choice to break the chain.
try to avoid pushing the pin all the way out, it's just bad form, but in this case it doesn't really matter since you'll be loosing several links anyway.
Step 3: Take off all the stuff you don't need
Derailers, front and rear go
It helps if you remove the cable first, sounds obvious but don't forget.
any cable guide you can get off
All the cables also
Step 4: Admire the nice clean lines of your new bike
Ain't it pretty without all those derailers in the way?
Step 5: Running the chain
The main problem with this design is that you really have no choice of gear ratios. The chain line chooses it, and you have to take it. With a derailer-less bike a straight chain line is extremely important. If it bends too much, it will skip off while riding and leave you in a bit of a lurch.
Step 6: Attach the wheel
screw on the wheel, but not to tightly, just finger tight is good enough for now. Try to have it as low in the dropout as you can.