Led Zep "Physical Graffitti" Cover - Why so expensive?

I have heard that Led Zeppelin’s “Physical Graffitti” album cover was the most expensive ever made by ANYBODY. (Well at least up until the time it was released). The thing that puzzles me is WHY ??
Just look at it - looks kind of ordinary - 1 letter of “Physical Graffitti” per window.
What made this thing so expensive ?

The original cover had a die-cut cover. The inner sleeve had the images that fit in each window. Making a complicated die-cut cover isn’t cheap (at least, it wasn’t back then). IIRC, it was also a gatefold.

I can’t believe that Physical Graffiti was even the most expensive Led Zeppelin LP cover to produce up until that time, let alone the most expensive by anybody! What about Led Zeppelin III, with the picture wheel? (Not an original idea, by the way; the first Soft Machine LP had a picture wheel cover in 1968.)

And don’t get me started on other artists’ covers that were out by that time and that were undoubtedly more expensive to produce, like Sticky Fingers, Velvet Underground and Nico, the first Faust LP (clear vinyl LP in a clear plastic silkscreened cover)…

Led Zeppelin had this genius deal where their record company had to pay for their cover expenses. That’s why they’d do multiple covers and other fancy stuff. They were total money-grubbing tightwads with a good manager.

Like Zep’s In Through the Out Door. It had a cover representing the POV of each of the people inside the bar. The album was then housed in a brown paper bag. I have a friend who used to have a used record store and had a complete set. He sold it on Ebay for about $200.

And the inner sleeve was impregnated with invisible pigments that only appeared when moistened. There was never any mention of this at the time, so people only discovered it if they happened to get the sleeve wet!

Biffy - I agree with you that’s why I posted this thread - why was Physical Graffitti so darned expensive?
One reason I heard was that the cover was printed using engraving plates (just the way money is printed). But is engraving THAT expensive to do? Then again, how were conventional album covers printed?
I remember the Rolling Stones album cover for “Satanic Majesty” used to have a 3-D photo. Now THAT had to be expensive. Maybe that’s why they discontinued the 3-D cover after the initial release.

I know zip about the album cover – but have to say, that’s my all-time favorite album. I bought it the minute it came out…
Of course, I threw all my albums away a long time ago, and bought CD’s. Kicking myself as we speak.