If you're not willing to spend the extra cash, get a .45.
The 1911 was not designed for the 9x19mm round. Switching a 1911 to 9mm is not a simple swap, with differences in both frame and slide components, all requiring extensive tuning. 1911s in 9x19 have a significant reputation for being extremely finicky without work. 9mm 1911s are also less in demand, further increasing their prices. The only signifcant demands in 9mm are competition guns (a la STI and others) and carry pieces (a la Springfield's EMP). There simply isn't a big enough market to try to put together a run-of-the-mill 9mm 1911; the only options are going to be on the higher end of the spectrum.
Contrast this with the .45s, where you can get an excellent, accurate, dead-reliable pistol for $600. It's just that the demand is there.