According to the press releases, the 40d was £899 RRP (http://www.canon.co.uk/About_Us/News/Consumer_Releases/2007/EOS_40D.asp) while the 50d £1200.
However Canon is doing something a bit unusual and introducing the 50d when the 40d has only been on sale for 12 months (rather than the usual 18 month cycle for N0d cameras), and keeping the 40d on sale for a bit.
I'm fairly certain however that within six months the 40d will be discontinued and the 50d will have dropped down to 40d prices. At the moment the 50d is nearly the same price as the 5d, which hasn't been refreshed for years.
That's why I'm planning on replacing my 20d next year - I won't use the camera much over the winter, and want it for the start of the new air show season.