Drop handlebars are a bit of a nightmare for me when it comes to riding in central London; and the old single piece quill stem is a barrier when it comes to putting bullhorns, simply because they don't fit through as you can't open them fully. So the way to do it cheaply is to cut off the drop downs and simply flip them over! So here are the photos of the drop downs turned into bullhorns, and leaving the same brake levers (to cut costs!)
Your local bike shop could cut the bars for a couple of pounds or a fiver if it's a fancy shop!