Is this the highest price ever paid for an LP?

Test pressings are made normally (stamped vinyl) to test the stamper for flaws I guess -- and generally given to various executives, etc.

Acetates are made before even a wax master is made. They are acetate-coated metal discs which are cut with a lathe (from the studio tapes) just like a wax master -- except they can actually be played (just a few times, because they're very soft), and are usually given to the artist for review/approval.
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According to an AP report, it was bought for 75 cents four years ago at a Manhattan flea market. Final eBay price was $155,401. [Not to shabby!] There is only one other acetate known in existence.

FatParrot you can find test pressings at record shows or on ebay. There not that uncommon I own a few in my collection. They are the very first copies on vinyl to come out of the factory then promo's then the mass produced. Most of them don't have a side # on them and my Million Dollor Babies by Alice Cooper the songs are sequed different than the ones that were mass produced.

It's a little over $20K now with three daysleft.