Shame you don't live near Manchester I'd have sorted it for you for the cost of parts.
I would put it more like £20 to £30 if a shop fits it.
If you want a fan to do it yourself have a look at
Microdirect.co.uk is the UK leading retailer of quality computer components and electronics. 
Look at Arctic fans, they are quiet and don't tend to go wrong. I run all my pc's on them