I have a few options for picking up a cyclocross bike. I am beat (not able to find anything) on the used/less than $600 range. I have seen stuff on web stores like for bikes gravity, and motobecane. I am not so sure if they are worth while with the options below. So, I want to reach out and get some opinions.
2012 Kona Jake 1000 (NEW)
2012 Giant TCX 2 899 (NEW)
2012 Redline Conquest 1000 (Slightly used)
2012 Cannondale Caddx 6 Tiagra 1000 (NEW) - Seems to be a good start
All City Nature boy 950 (NEW)
Go SS as it's:
a) less expensive,
b) lighter (if that matters to you),
c) simpler to learn on (no gear selection mumbo jumbo to learn),
d) less to keep clean during races.
Go with something with at least 105 (or Rival, not a fan of SRAM though), Ultegra is a great performance value if you think you will be racing in years to come, or if your backup plan is to use the bike to commute or road race on (yes, I know several people who road race on their cyclocross bike). Don't worry about the frame or the brand, you will not get into a carbon frame at this price point anyway, so AL is AL. Check the geometry and ride the bike!!! A year or two old used bike is usually a great value and plan on paying about 50 - 60% of MSRP. A used bike may also have several upgrades that will save you money in the future. I would stay away from a single speed its a whole other ball game. You might want to also consider a single chain ring in the front, with all the gearing options it can be a great way to lighten the bike and make racing less complicated and mechanical issues to a minimum Front chain ring drops suck and are prevalent with new racers. You would get a WAY better bike if you could up your price by about $200, good used bikes start at about $750 if your lucky. Be patient and wait for the right bike. Make some low ball offers (but not too low to piss off the buyer) in the beginning you would be amazed at how some people will drop their price for the right person. Also, don't buy cause you think its a great deal, buy because its the right bike!