You are guessing. Many contractors have a minimum service call rate higher than $100.That breaker is about $150, plus another $100 to swap it out. I have done them for customers before.
Not to mention the OP never told us if he had a disco. Or did the contractor have to pull the meter.
Since the pictures are either sideways or the OP is in Canada, we have no idea how to price this from our keyboards.
While $750 sounds high, it actually could be low. For the OP's location.