I'm not sure what you have seen for £4.50 but I think it will not be enough.
SATA drives use different power connections, and data cable connections to IDE drives. You need to be able to covert both.
A quick google found this site, which shows what you might need (not saying it's the best option.
http://granitedigital.com/catalog/pg...idgeboards.htm
By the time you've paid those sort of costs, you might as well have bought another HD and keep the existing one for backup purposes.