Originally Posted by crankholio

If you actually did it for zero cost, it's probably because you have a big parts drawer, and aren't counting any cost for those.

Some ghetto-rigged examples I've seen:

• Leaving a multi-speed cassette on the rear.
• Using ramped and pinned chainrings when the chain line isn't perfectly straight.
• For older bikes with screw-on multi-speed freewheels, replacing the multi-speed freewheel with a SS rather than doing the proper thing and getting a new wheel.
• For vertical dropout frames, trying to get the chain length just perfect and omitting any means of adding tension.
• Using an old derailleur for a tensioner.

If you happen to have an older road bike with horizontal dropouts and a freehub, you can do a reasonable conversion with a cog and spacer kit. If you trust any 'ol off brand for those things, you might find them for $20-$30. Something better is more like $70-$80. If you have vertical dropouts, you'll need a tensioner, so add $50 for a good one.

If you have vertical dropouts and you want to ride mountain or fixed, you really should avoid a tensioner and use an eccentric rear hub. So that'll run around $300 for the wheel on its own.