This is an instance where you'd really need to see what's there, either good pictures or being there to see if it is a problem. The clamp can put a dent in the insulation and not affect operation, but if the insulation is actually cut, that is a problem. In many situations, the wire is supposed to be anchored, so the fact that it can't move is not necessarily an indication of any problem. As to price, also hard to say. 10g wire is expensive, and some of the material costs would depend on how far they had to go if it was determined it needed to be replaced. What size circuit breaker is used for the WH and what does the data plate on the WH say it requires in amps or wattage? 10g may or may not be the right size. If it isn't, then it should be replaced, regardless.