Greetings and welcome to the forum.
There are definitely a few costumes that aren't too extremely expensive. X-wing pilot costumes aren't too bad and you can buy pretty much everything already made and ready to go. Jedi can also be fairly cheap depending on the boots and lightsaber. Rebel fleet troopers are really cheap, in fact I think the most expensive part is the helmet (which would probably around around $100, if I remember right).