Less than $50 to do it right.
Ingredients of a typical SS conversion –
Cog, spacers & a tensioner – http://www.amazon.com/Single-Speed-Conv … B0014X6TM0
New chainring bolts (for only one ring) – http://www.amazon.com/Origin8-Single-Bi … d_sim_sg_8
Sometimes you get lucky with the gearing & the chain fits just right without the tensioner. SS’ing isn’t for everyone and has a lot to do with the terrain. It’s a good idea to pick a single gear & go for a ride first to see what it’s like. Simple as it sounds sometimes people discover that not having at least a few gears is more pain than it’s worth.