The OP did not ask about the cost of the cables, some of you can easily pay absolutely crazy amount for a short piece of super thin litz wire (for internal part of the tonearm).
He asked about the cost of some pro to do the job.
As I said it depends on the tonearm, if all you need is to disassemble some tonearm parts to remove 4x25cm thin wires from sme type bayonet to DIN connector then it can be very easy. Copper Cardas or Discovery litz will not cost you more than $60 for 50cm (which is enough for two tonearms).
I don’t think this job can cost more than $100 in the real world!
P.S. If your tonearm is the one without removable headshell and without DIN connector inside then it’s even easier, but in this situation you need one phono cable for internal and external parts of the tonearm in this configuration.
He asked about the cost of some pro to do the job.
As I said it depends on the tonearm, if all you need is to disassemble some tonearm parts to remove 4x25cm thin wires from sme type bayonet to DIN connector then it can be very easy. Copper Cardas or Discovery litz will not cost you more than $60 for 50cm (which is enough for two tonearms).
I don’t think this job can cost more than $100 in the real world!
P.S. If your tonearm is the one without removable headshell and without DIN connector inside then it’s even easier, but in this situation you need one phono cable for internal and external parts of the tonearm in this configuration.