It is one of the defining albums in the history of rock music and sold inlarge numbers. Even when it was released, Deep Purple were a big band, so there are loads of different pressings in large numbers. That's why you see it for a few pounds in every second-hand record shop.
However, there is a collectible copy to be had. It was initiallyreleased on Purple Records, matrixTPSA 7504 with alaminated gatefold sleeve and lyric sheet.
A mint copy of this is currently valued at £30.00. The really hard to get version is the Quadrophonic copy - which is the same in every respect except it has a Q in the matrix number.
I never really got the point of quadraphonic and it was only around for 3 years or so in any meaningful way but it means the records are often collectible despite being million-selling albums.
A Quad copy is currently valued at £60
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