Paul McCartney signed High in the Clouds sell for about $800-$1,000 and those were signed at book signings and there are thousands. Most very nicely signed, especially the US edition, but they're still far more common.
There are only 250 of these books, so I think Goodcat is right at $1,000+. I wouldn't be surprised if it broke $1,500.
Signed copies of High In The Clouds are indeed much more common. I've only seen about 20 signed copies of the standard edition of Blackbird Singing. Here's my copy: