2004 Mazda 3 P0456 Fault Diagnosis: How to Identify and Fix EVAP System Leak

I'm not very knowledgeable about cars, but I don't want to spend hundreds at a mechanic when I might be able to fix it myself. I've read that OBD2 code P0456 on a 2004 Mazda 3 can indicate several potential issues — most commonly a faulty gas cap, but also possibly small leaks in the EVAP hoses, fuel tank hoses, purge valve, or vent valve, or even a leak in the EVAP canister. My main question is: how can I accurately determine which component is causing the check engine light to come on? What would be the approximate cost to repair it? And after fixing the issue, will the check engine light turn off automatically, or do I need to clear the code using a diagnostic tool? My vehicle has a 2.3L engine and has accumulated 145,000 miles. Any advice or guidance would be greatly appreciated!