Wickes over at London road are doing the same butt as mine (plot with greenhouse) for just over 20 quid. This is a good deal as it comes with a stand, tap and drain feed system.
Remember that water is a scarce commodity (might not feel like it just now!) so utilising rainwater on the plot is a great way to help the environment. Also rainwater in a butt is not as cold as mains water which has been scientifically proven to benefit young plants by not "shocking" them as much.