SS isn't attractive to a lot of people, just the numbers of riders alone will tell you that. But if you are compelled by "whatever" it is that makes SS seem like fun, go ahead and give it a try.

"Whatever" can be as simple as reliving the old childhood days on bikes without gears, it can be less maintenance, less tech, or a desire to do it the hard way. Having a good time on a bike is reason enough.

1000 dollar bikes with decent front suspension are going to be used or built with stuff you already have if you want a good wheelset. You could get a Redline monocog flight or Nashbar SS and then buy a sus. fork or buy something like a Kona Unit with a rigid fork brand new for 1000 bucks. MTBR does have more of a dedicated mtb SS forum to read through.

Getting passed on a climb by someone on a geared bike is a small concern, they usually take a smaller gear, then sit and spin up that hill, whereas SSers have to stand and mash right on up. Singlespeeders get beat on the flats after they spin out the limit of their chosen gear or on big descents on rigid or hardtail bikes, but not so much on climbs.