How much does this generally cost and would it tell you the level of deafness?

Thanks
J

It not only tells you whether a dog can hear in both, one or neither ear, it can also tell you at what decibel range. The cost depends on the age of the animal (whether a puppy or adult - adults generally need light sedation whereas baby puppies don't) and which testing centre you use.

Information here.

You should also get a printout of the result, in graph form, at least my friend did wjem her litter was tested at the AHT, together with a certificate.