In my experience on E-bay, this is what these cards are worth:
Gandalf, Leader of the Company (p) (foil) [Promo] - There's one for sale on E-bay, Buy It Now for $10.00. But I got mine in an auction for $7.00 (not including postage and packing).
Faramir, Prince of Ithilien (p) (foil) [Promo] - I paid $58.00 for mine on E-bay (not including p&p). I got lucky, though, because there were 2 up for auction at about the same time, so I think that I got a good price. I have seen one go for as high as $80.00, but that's not the average. I haven't seen any of these up for auction for a while. I would say about $60.00 to $70.00 is about average.
Aragorn, Isildur's Heir (foil) [Rare] - There are 3 of these up for auction on E-bay, all Buy It Now. They range from $6.00 to $10.00 in price (not including p&p). I haven't watched any auctions for this card for a while, so I don't know what it would go for at auction.
I'm not saying that these are definitely what you should pay for these cards, only what I myself have seen. Other people might have seen different prices than these, just my 2 cents worth. I hope that this helps!