I agree with Darryl, actives are by far the best bang for your buck at around £250. I would go for the Alesis Monitor One Active Mk2- very, very good for only £220 brand new or even cheaper off ebay used, they pop up quite a bit. You just need a source with level control.  I'd put a pot in a box for level control and use a second hand CD player, maybe something like an entry level Marantz?

http://www.dv247.com/invt/9490

http://cgi.ebay.co.uk/ALESIS-M1-ACTIVE-MONITORS-SPEAKERS-technics-wharfedale_W0QQitemZ7547905589QQcategoryZ21145QQssPageNameZWDVWQQrdZ1QQcmdZViewItem