Today I bought a clarinet from Netto in Newmarket. These had been £59.99 in 2008. They were marked up with a £49.99 ticket, but it was reduced to £19.99. There was one left. Its probably a clearance item, so you might not find them in general.
I've had a read around, and the general advice is that its better to learn a better quality instrument. However, for a new clarinet, that is likely to cost £150-200, or £75 second hand.
However, I just wanted something to try out, without making a big commitment. When i first tried it, it took me 15 minutes of blowing before I got a note out of it, but after a bit of googling, I worked out how to get it to work. I don't think it was a problem with the clarinet, more the user!