This thread feels so Fixie/SS.

Parts needed are: BMX freewheel 16t ($13), BMX chainring bolts ($8), rear axle spacers (maybe).
Tools needed are: 5mm allen wrench for chainring bolts, tool for removing/installing chains, cone wrenchs, open end wrenches, freewheels tools.

1. Its always cheaper to start with a complete bike. Always.

2. Find a bike that fits you with 700c wheels and a double crankset up front with removeable chainrings.

3. Remove the F&R derailleurs, shift levers and cables and existing freewheel.

4. Remove outer chainring, install BMX chainring bolts. Measure chainline.

5. Remove 6mm of spacer from gear side of rear wheel, lightly install BMX freewheel. You now have a 120mm spaced rear wheel. Center axle.

6. Squeeze rear frame spacing down to 120mm, install rear wheel.

7. Measure rear chainline. If its different than the front move spacers around to achieve proper chainline.

8. Re-dish rear wheel.


There are other ways of doing it but this is the least expensive way if your dealing with a scew-on freewheel. Its possible to convert leaving the frame spaced at 126mm but you'll need a very narrow BB to get the proper chainline, shifing spacers around only gets you so far. Starting with a cassette hub'd bike is the easiest and least expensive, aside from the cost of tools your looking at $8 for BMX chainring bolts.