not sure where to start with my costume

This will be the first costume I ever made. I am not sure how to start out I looked online at the fiberglass helmets and the price is too much for me. Maybe I could modify a $50 helmet I saw on buy cheaper.com. Do the cheap costume store helmets have potential to be modified to a good looking helmet?

Yes they can but it can be quite a bit of work and the cost to modify one might end up being as much paying for good accurate helmet. The helmets run in difference sizes though so you should be sure they'll fit your head before buying it. Check out this thread for helmet sizing and it should show you the wide range of helmets around. http://www.thedentedhelmet.com/f23/helmet-sizing-thread-45911/

thanks I will check it out