I've been lurking on the FG/SS forum for awhile - love all the eye candy.
I don't actually own a FG/SS bike anymore (used to have an SS mountain bike), but I pretty much run my road bike SS as I don't really shift out of the gear I'm in now. Anyways, I found an old Norco conversion for $125 on CL, and I was thinking of maybe getting that as a beater bike for campus and such (so I don't have to worry about my Kona JTS all the time). However, I was also thinking if I should maybe just save that $125 and put it towards an IRO or Eighth Inch Scrambler eventually.
If I go the IRO/Scrambler route, it wouldn't really be used as a beater as much as a short-distance commuter and possibly a velodrome bike
beater - probably used mainly as a short commuter, bar bike, etc gaurnteed will cost you more over time as the components will get worn out faster than those on a new bike. think tires, drivetrain, bar tape, etc
IRO - good city bike, good on trails, lightweight but solid, better components than the scrambler, IMO the best all around bike around at its price point, very versatile bike
scrambler - flashier bike if that's what your into, heavier than the IRO and possibly more solid, will take bigger tires than the IRO, still seems like a pretty good bike to me. If you are building from the frame up the scrambler is $100+ cheaper than the IRO which might factor into your decision