You can renew EAD yourself. I did, and many others did.

Why pay $2800(shocking price). EAD application is quite straightforward.Go to PJiang's blog to get the check list:
http://blog.wenxuecity.com/blogview.php?date=200706&postID=42162

Normally, you renew your EAD 90 days prior current one's expiration date.