Thanks Fletch! Exactly this is our problem, how much should me spend? We went to a local music shop in London (Soho, Denmark Street) and a guy who is working there told us the same as you now. Very interesting and helpful! I first thought he wants to rip us off, but now...I don't think this anymore. Haven't told him then.
I think we'll go for a real drums kit. But which one and what price range, I'm still confused here.
There is a great store not far from us
http://www.propercussion.co.uk, but they will probably give us another opinion!
On the other hand, if our son will be serious with the drums, he will torture us in the house, I hope not our neighbours too. How loud is an acoustic drum kit?
One more question, does the rule apply for drums as well: You'll get what you've paid for?