You can measure it how you like - the quality of music, the quantity, the diversity, whatever, the only rule is you must have paid for it, no freebies or illegal downloads etc.
Mine would either have to be a box set of classic blues artists made up of ten CDs, each a collection of recordings by people like Leadbelly, Bessie Smith, Howling Wolf, BB King etc. One of the discs is the complete recordings of Robert Johnson. I can't find it on Amazon, but it cost me £10 - BARGAIN.
My other option would be the Essential Bruce Springsteen collection which I got as an introduction to the Boss - three CDs covering his whole career with all the songs you'd expect as well as a load of obscure stuff - all bought from Fopp for £3. Less than the price of a pint! Now that's value.