I made the mistake of getting a $200 single-speed bike from Performance with the intention of making it into a fixed gear. The stuff on it was so cheap I have spent $200-$300 just to make it rideable (read that as a new 2nd hand crank set to accommodate the standardized pedals, crank set adapter because it was an American sized BB, new fixie wheel, new front wheel because it was junk before, various cogs to get the right size, and I'm still not done!) And that isn't even all labor because my friend is an LBS guy and does a lot of the work I can't do for me for free.

It's always better to put the money into the bike upfront. Quality goes far!!