my 2cent

You can ask a general attorney to see how much he charge for a green card. I know a few years ago it cost only $1000 to $2000. So you may ask the attorney over charge. Usually the company can get discount from the attorney if they give all the case to one attorney company.

And you may have room to dispute. If the company prepare to charge that fee, it may disclosure to you the real cost in frount. Like you buy anything you need to know the price in frount. When I get my freen card, the company allow us to use any attorney but pre-fer the company attorney.