I went to the Chorley one yesterday and it was £6 before discount. I noticed while I was there though that wash 1 is only £1.70. I didn't realise it was so cheap so I'll be going more frequently now.
The rain comes, the car gets clean :D
I think that with the discount, this is £3 at the Southampton IMO. I took a layer of paint off my car with a kitchen sponge a while ago (don't ask), so no longer care about my paint work, although I've never noticed it doing any damage. The car wash does, however, like to eat aerials, so make sure you remove it before you go through if you like the radio.
Different prices at each site. Average is probably around £7. Thanks j0nY90