Unfortunatley its not a free service but you can go to Fiverr and explore there for proofreaders and editors. Its a freelance website where people offer their varying talents for whatever prices. I am a little hesitant to recommend it since there isn't an absolute guarantee of quality, but there are a couple of cheap options you can find there if you really feel your work needs an outside pair of eyes. Make sure you research a little though, everyone on there is a freelancer and they all have varying degrees of quality on their work