Value of 1958b DLR Map?

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I am not soliciting buyers but if you are interested, you can PM me.

My friend Mary found her large poster map of the DLR in her parents' house. She had forgotten all about it. It was still in the original mailing tube addressed to her, postmarked 1958.

Here's what she e-mailed me:

It’s a 1958b map. There are also “a” and “c” versions. Supposedly the “b” is the rarest. There’s one for sale on Ebay now for $300.00. An auction just ended at $770. They also offered some photos and a ticket stub with the map.

At some point, the map had been scotch taped to the wall but the tape is only at the very edge of the margins. Otherwise, the map looked perfect to me. It also looks like it was printed yesterday, since it's spent most of the time since 1958 rolled up in its mailing tube.

I wish I could buy it. It is a thing of beauty.

Any idea about value or thoughts on how and where to sell this?