We picked up a "Bush Shower" in Oz. Cost about £7.
They seem pretty common over there, so try one of the Disposals stores that has a website. You might have to pay a bit in shipping etc, but it should still be pretty reasonable.
The solar showers are useful - especially if you are working from a camp or vehicle. But if you dont mind heating the water with a fire - you should be able to get enough water from 2 crusader mugs topped up with some cold to make it reasonable.