Popped into PC world looking for a cheap and basic mouse for the old back-up computer, and found them selling 'Elonex' branded wheel PS/2 wired mouse for 49p each. They are basically the PCline mouse (£4.99) see photo, with 'Elonex' printed on them instead. I guess they are selling them cheap due to Elonex going into administration last year?
You need to download the Microsoft Intellimouse driver to get the wheel working. I found them in my local store in Brighton in the brown box components section of the shop. Saved me £4.50!
Note: Very similar to PCline mouse, but not exactly the same!