Hi Jonathon,
Welcome to the forum. Great to hear that your son is wanting to sail a Cherub. They are great fun boats and would be the perfect next step up from the 29er if they are not wanting to go down the Olympic 49er route. My wife and I currently sail our older Cherub at Netley, and so I can confirm that the club is perfect for sailing a Cherub as there is plenty of space to rig, and the launching and recovery is easy from the beach. Historically, there have been Cherubs at Bough Beech in recent years too.
As you will probably see by the lack of 'For Sale' boats on the site, they are in pretty high demand at the moment, with boats generally changing hands before they officially hit the website.
£2000 should get them a decent older boat which may have been converted to the 2005 rules (larger sails and twin trapezes). I would expect boats built after 2005 would be changing hands for £3k plus still. The beauty about the Cherub is that it is a tricky boat to sail and so it is still possible to do well in an older boat if they are willing to put in the sailing time and really master the boat handling. Races are won and lost at the start and the turning of corners so there is plenty of time to be made up against other less well sailed boats!