Unfortunately, the lovely pink colour will drop out as the wine ferments.
I don't have a source of free rhubarb any more so had to buy 3lb for £3. I'm not sure how this compares to the supermarket price but it's grown locally and, though not certified organic, is grown without chemicals. Add this together with 35p (approx.) for the bananas and £1 for the sugar, it works out at 72p per bottle. Not as good as 20p obviously, but cheap all the same.
More on rhubarb wine can be found here