Is $400 to replace a bad breaker inside the house a fair price?

After a storm, my AC unit started tripping the breaker. I initially called a technician who diagnosed a bad breaker and quoted me $400 for the replacement. I replaced the breaker myself, but the issue persisted. I then found a burn on a connection in the disconnect switch, so I replaced that box. The unit worked for a day, but then the breaker tripped again. My dad checked the unit's amps and ohms, which appeared normal, and the unit itself is only a few years old and seems to be in good condition. I'm trying to understand why the breaker keeps tripping and am wary of technicians who seem more interested in selling services than fixing the problem. I'm looking for advice or suggestions to resolve this ongoing issue. The power did go out during the storm. The technician who came out didn't check much on the unit before concluding it was the breaker. I'm considering checking the run capacitor if the issue reoccurs.