There's a vintage Leak Stereo 20 somewhere in the Private Exhibitions for around £500.
Don't be put off by the age, they are amongst the more reliable valve amps. The sound quality is excellent and the 'mere' twelve watts is actually pretty punchy.
Handily, the Leak can be used effectively with a modest passive pre-amp very successfully. I've owned three of them and wouldn't mind another. Great bit of kit.