Officer's uniforms are real easy. The boots are probably the most expensive piece. But I would say that if one were frugal enough, they could get an officer done for about $300, that is if you don't mind making the uniform from scratch. If you buy the costume, it would be a lot more, since upgrades are always something that would need to be done.
I'm a former Imperial Officer of this garrison. If you wanted to go with Imp Officer, I can help you out. But like Cooter said, don't buy anything yet, until you have figured out exactly what you are wanting. This garrison is committed to looking out for its own, including their pocket book. So, listen to the advice given... you won't ever be steered wrong, I can promise you that!
I can definitely help you with that officer belt (leather worker here), since I have made a few.
Good luck!
- Bill