How can buying a new hard drive be cheaper than fixing a existing one? There is something seriously wrong if that's the case.
There has to be a lot that goes into making a hard drive. They would have to buy all the raw materials, turn that crap into parts of the hard drive, pay employees to manufacture those parts into a actual hard drive or have a machine do it both of which will cost a lot of money, then pay employees to market it and sell it to a distributor for dirt cheap and then offer a 3 year warranty on top of all that and fix it for free when something goes wrong.
Yet somehow that is all cheaper than having them replace a part.
Id imagine its because they buy the stuff in bulk, and manufacture it in large groups using robots. Whereas repairing it requires actual humans to diagnose the problem, swap parts out, and give another warranty on their work.
If the drive is out of warranty then there is nothing you can do to fix it and it is fit for the bin and next time get a drive with a five year warranty. Before you throw it away though open it up and take out the magnets, they are great fun to play with and look on you-tube at some of the great projects people have done with dead hard drives.