Elgar enigma/ Picture at an exhibition

Kudos to you for being involved in your son's music education.

Several fine recordings of Pictures as already mentioned. But, for me, to really understand this music the performance needs a Russian sensibility. The Valery Gergiev reading with the Vienna Philharmonic is hard to beat. I also encourage you to have your son listen to a recording of the music as originally composed; for piano. This will broaden his understanding. The Sviatoslav Richter recordings are very fine.

The price has gone up I didn't pay anywhere near that for it.

Good suggestion from Frogman to listen to the the Pictures as
originally written for piano.

But as to needing a Russian orchestra to really get the full
sense of this orchestral work, remember that the orchestral
version most often performed is the orchestration by the
French composer, Maurice Ravel.
.

A second for Monteux and LSO on the Enigma,

A Pictures recording with a really great orchestra would be the Ormandy recording with Philadelphia:

http://www.amazon.com/dp/B000F6YW2Q

(There's another recording on RCA, but I'm referring specifically to this one on Sony.)