First, I must admit that I'm a roadie. Mock away.

.....

That done and out of the way, I'm using my road bike to commute, and I'm afraid I'm thrashing the poor thing; thin aluminum tubes are definitely not fond of ill-maintained city streets. I want to put together a fixed gear bike, but I'm on a hella small budget. Could I scrape one together for under $300 US? Less?

If you were going to do it, how would you?

TIA