Very unlikely to be cheap. To do this properly you pretty much need a clean room (or at least a slightly-clean room) to minimise the chances of dust and other environmental pollutants.
With the scale that these things operate on, any initial physical damage is likely to lead to physical damage to a lot of the device. If a bit of a head had been damaged and is out of alignment, then every time the heads scan across the disk more and more damage will be caused to the media. Bear in mind that the heads scan across the media pretty much all the time when in use and you get the picture.
If it is business valuable data then you could try a company called Renaissance (in Dun Laoghaire I think) or RITS. I think these companies do some of this type of work, but I could be wrong.
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