Hi, can you put a scan of it on and I will tell you if the signatures are genuine. I have been a Newcastle United collector for over 40 years and have an extensive collection of autographs.
I also have the shirt David Batty wore in his last game for Newcastle signed by the whole team on the white stripes.....framed and on my office wall. As I used to work in football I was given the item by one of their international players.
I also have many signed Bobby Robson and Alan Shearer items.
I could not put a price on your shirt as it, quite simply is worth what a buyer wants to pay and due to many faked items on auction sites I would be surprised if your reserve price was met as there are too many dealers selling similar items.
As for certificates of authenticity, they are not worth the paper they are written on as anyone can print them.
I have a few signed items in my ebid shop which are all 100% genuine as I either got them myself or from the leading autograph dealer in the country but the only way anyone can be 100% sure is to get the signature/s personally. I have sold hundreds of signed items on the other side and had many repeat buyers who knew they were receiving 100% genuine items.
http://bertgees-bargain-buys.ebid.net
Good luck with the shirt and I hope you get what you want for it.