Sorry to hear of your continued woes with your Macbook Graham, that does sound pretty pricey.
Depending on the model of your Macbook, the HDD should be fairly straightforward to replace...some just require the removal of the bottom cover with 8 (I think) screws and the HDD, memory and battery are right there.
Depending on whether or not you want to do it yourself, you could always consider another Mac specialist such as
https://www.macfixit.com.au
I don't expect it's any consolation, but a friend of mine used to work in an Apple store, and they routinely seemed to bend the rules to fix machines and make customers happy despite corporate rules. Sorry to say it doesn't sound like luck was on your side that day!