Very roughly £4 per reed as far as I can remember. Reed manufacturers tend to prefer dealing with businesses over private customers, so they’ll normally only be interested in selling several sets at a time. I bought 10 sets because I had a few things to try out!
They don’t take any more air to blow. One shortcoming of these accordion style reeds, and I’m not sure why, is that they choke quite easily with moisture build up, maybe because of the thicker tongues. It’s something I also find on the Vibrandoneons.