If the PAT failed calibration, this means an "as found calibration" (as delivered) has be carried out where it was discovered that measurements on the 100mA bonding range were outside the manufacturers specification. If this error had been within the allowable adjustment range, the PAT would have been adjusted by the calibration technician to restore it to within the specification. A final calibration would then be performed to certify the PAT is within the specification on all ranges.
However, your PAT was obviously not able to be restored to within the specification without component changes, hence you have been quoted for the repair work required and the subsequent calibration. The price you have been quoted is average for the type of repair and calibration. You may be able to shop around to find a better price, but i think you will be hard pushed to get it much under £150. A calibrated second hand PAT of similar quality and ability, in good condition may well cost a similar amount, personally I would be tempted 'to bite the bullet' and keep the 'devil you know'.
