A still sealed Buckingham Nicks album can go for 100$, I believe. As soon as you take the shrink off, though, its value goes down to 50$. The hardcore collectors only buy the still sealed ones but of course they never open them.
I had to order the thing from the States (since I believe no one in this country would have it), and even still it has slight surface marks. 25$
only though.
As for the seven inches, not much luck here. The only unusual thing I've been able to find is a Japanese "Everywhere"/"When I See You Again". You can spend a lifetime collecting all the variants of the regular releases.