I've hunted round for a reasonably priced bunk bed frame and came across these which seems a good deal. Cheaper than fleabay prices even. If you make up the order to £100 then you can use the 750 points code (TDX-FXK7) which means you'll get 930 points (= £37 in deals).
This is for the frame only and doesn't include mattresses, but does have fairly good reviews.
They also have some reduced mattresses but http://www.mattressman.co.uk
appears cheap too...
Hope this helps someone.