I have one of these, less than 15 quid, temperature and cadence, not wireless but no real issue.
It's been great and the temp is accurate.
http://www.cyclestore.co.uk/productDetails.asp?productID=14292&categoryID=99
Cheers for that I've just ordered one. Seems perfect for what I need for the price. I wasnt going to bother with a cadence one but might as well for that money!