Well, you won't get close to his signature Martin... but I would say for him to look for a martin in that price range. I personally will never buy another acoustic besides a Taylor... but Martins and Taylors are two different tones... But Clapton uses Martins... so tell him to look for a Martin in his price range and have him try to play different kinds to see how they sound and feel.. Martins are known for high action and feeling a bit dry.... but they are awesome guitars nonetheless.
If he wants, check out a Taylow too... and compare. The tone will be different... but they're top of the line... I think he should be able to look at a 400 series or 300 series Taylor for around 1000 USD... which would be around the 1600 aussies range.