Ok so currently I have a Behringer BXL450A (http://www.behringer.com/BXL450A/index.cfm?lang=ENG). It is 45 watts and that is no longer enough power for my needs. I need enough output to be heard over a 120 watt guitar amp, and any more power would be nice. I'm thinking anywhere from 200 to 600 watts might be good. I have no money, but I can save up. I'm trying to decide whether buying a more powerful speaker or a new amp all together would be a better investment.
New amp!

Well, I don't know the quality of Crapinger's bass amps, but if they're anything like their guitar amps, i'd get a new amp.

As for which amp, I know nothing of bass, so i'd wait for someone else to chime in.
Call me Wes.
Fender American Deluxe HSS Strat
Chicago Blues Box Roadhouse
Bad Cat Cougar 5
1957 Gibson GA-5
Ceriatone 18w TMB Combo
Hughes & Kettner Tube Factor
Various Ibanez TS9s
Weber MASS Attenuator
I would say a new amp. Behringer tends to rate their amps at peak watts, not at RMS, which is how they should be rated. I think something like a 300w would be good. Drfinately save up for something good.