I once bought hanging baskets for New Cross Gate (don't all gasp at once!) and the actual hardware cost is minuscule and the planting only a little more. The major cost is getting them watered regularly (without which they would die very quickly!

I was also a bit surprised to hear that green folks are actually against hanging baskets as they are not "sustainable" i.e they are very high maintenance, use a lot of water and, in the past, but maybe not now, used peat compost. The current preferred method for civic planting, I now understand, is troughs.