My blog was written with people like you in mind; very budget conscious
I'm in that boat too. linked in my signature (3lists)
1) go read it, scroll to the bottom and start with the planning worksheet, read up through all of them because they will all help with that character.
2) you can absolutely thrift 3/4 of Green Arrow, only his cape is likely to need to be made from scratch. While you aren't likely to find anything leather in green, you may find light natural toned leather, which you can dye green yourself (leather dye is VERY DIFFERENT from cloth dye, but it's as easy as paint).
3) Don't neglect yourself in the costuming process, it's more fun to cosplay as a team. I have two daughters, and they agonize over what characters to do, because they both feel the need to be a 'set'.