I just converted a few days ago and im LOVING it. I pulled the old 5 cog freewheel off and replaced it with a 17t BMX freewheel. For the front, I used the small 40t chainring moved to the outside. I ground down the chain ring bolts with a dremel to make them fit with a single chain ring. All said, Ive got about $20 in to the conversion, and about $170 into the bike total, including new tires and tubes.