The pic of the helmet may look good, but they are far from it. The size of it is all wrong, and they warp big time in the heat.
For example, coming from experience.
This is how Rubies advertise their Chewbacca costume
This is how it really looks
And this is how a real fan made Chewie should look
My point is, don't believe everything you see, or even read on Ebay. Even if they say 501st approvable, doesn't mean that it is.
You've said that money is tight. Don't throw it away on eBay Rubies crap.
Sign up at the relevant detachment for the costume you are interested, read lots then ask questions. Read the CRL for the costume, and read it more than once. Then think about spending money.