Hi Amr,
I have been collecting US-coins by years for several years.. As far as I still remember the key date coin (so the most expensive coin of the series) was the 1909-S V.D.B. coin.. It has the designers initials on it.. It's expensive, but I wouldn't think that it's impossible to be complete with the series.. Maybe somebody knows another expensive coin and the value of the VDB coin?
I would like to send you a little book that will definitely help you to know what coins are more expensive than others.. It's a 1999 Red Book covering US coins since 1616. Sure it's old, but it covers all the old coins and for the newer ones I'ld have a little surprise for you
Just tell me whether you would like to get, then I can put it aside for you when we have a trade, of course it's for free
Best wishes
Marvin