Lots of options. Before plunging in head on I'd recommend you just convert your existing bike to SS, that's the least expensive way to try it out. Read how to do it here: http://www.singletracks.com/blog/mtb-re ... nglespeed/
I do think you'll like riding SS, a lot of folks do: http://www.singletracks.com/blog/uncate ... -a-chance/
The Civilian Luddite is a budget option complete: http://www.singletracks.com/blog/mtb-ge ... al-review/
You can also look around for a used Redline Monocog. The base Monocog sold for around $500 new. It's a tank, and had rim brakes, but you could find one for cheap I'd betcha. I'm not sure if they even sell the base (ie cheap) Monocog anymore.
www.SouthernWheelworks.com - Custom wheels designed and built just for you, by hand.