Airline prices have been increasing over the past 2 years as the airlines attempt to recover from the damage caused to the travel industry by the pandemic. 2 years ago it was possible to find flights from many cities in the U.S. to Zihuatanejo for as little as $500 USD. Now those same tickets are approaching $1,000 USD. There is an option, however, that many people may not be aware of that can save quite a bit on airline fees but it requires a little extra work. Volaris (www.volaris.com), a Mexican airline, has direct flights from Tijuana to Zihuatanejo a couple of times a week. Those tickets can be found for as little as $100 USD round trip. Once you know what days you can catch direct flights from Tijuana you can purchase flights into San Diego and then take transportation to the CBX crossing (https://www.crossborderxpress.com/en/requirements) . The CBX crossing has an entrance/exit on the U.S. side that enters directly into the Tijuana airport so there is no need to go into Tijuana or try to find your way from a border crossing to the airport. You will still have to go through customs and immigration procedures but the process is streamlined and many find it quite a bit easier. There is a $20 USD fee for using the airport crossing. You will also need to factor in that there is a $560 MXN peso tourist fee for stays of 7 days or more. Another factor to consider is that Volaris charges for all carryon bags as well as checked baggage so you will need to make sure you understand those costs when comparing overall costs of going this route.
So in summary, find a flight from your preferred airport to San Diego, then take an Uber/taxi to CBX (Tijuana airport border crossing) and then get a flight from Tijuana to Zihuatanejo and have a great vacation in the sun!