Here is my first attempt at SS/FG and since I've seen a bunch of inquiries about how cheap it can be done figured I post mine as an cheapie example.

Found this bike with a free sign on it a week ago. It was missing the front wheel and one brake pad, but otherwise complete. Took it apart to frame. Threw away crank, pedals, bb, ders, brake pads, seat. Cleaned and reused the rest.

Here's what I bought:
Ultegra bb - $45
HS bearings - $4
Aztec brake pads - $16
Wheels Manufacturing single cog spacers - $12
Campy 12t lockring - $19
Single chainring bolts - $10
Campy chain and cog - free (lightly used from lbs)

Here's what I already had laying around:
Ksyrium Elite wheels
Rolls Saddle
Speedplay pedals
Ultegra crank w/chainring

Had first test ride and it seems pretty decent for just over $100. Will change seatpost, stem, handlebars, brakes (original levers are crap) and centerpulls are a PITA imo. If I like it after a few rides I'll invest in fixed rear wheel.