What is a Pitch Raise?
First things, First. If a piano has gone without tuning for an extended period, its pitch has likely dropped far below the standard pitch of A-440. This means that each of its approximately 220 – 250 strings needs to be tightened considerably, adding tremendous additional tension to the piano’s overall structure.
The problem with pitch raise piano tunings is that as each string is tightened, the additional load (tension) causes the pitch of previously adjusted strings to change. Thus it is impossible to make a substantial change in pitch and end up with a fine, accurate tuning in one step. Instead, a process called “pitch raising” must first be done, in which all strings are raised to their correct average tension levels. (Likewise, when a piano’s pitch is higher than standard, a pitch lowering procedure must be done to reduce string tensions to approximately correct levels.) Only then can the piano be accurately tuned.
In other words, accurate tuning is only possible when all strings are so close to their proper tension that only small further changes are needed during tuning. These small changes then do not disturb the tuning of other strings.
So Why Does it Cost More?
In short, a “pitch raise” costs more due to the additional time required to completely tune the piano. If it has been years since a piano’s last tuning, multiple passes up and down the scale are required to achieve a stable and fine piano tuning.
To attempt to tune a piano that has not been tuned for an extended period without following this method will result in a tuning that is all over the place as far as pitch is concerned.