It doesn't have to get too expensive. You will however, need to get your hands on a capable scanner (or pay a shop or dealer) to actually see what's (not) going on during a start attempt. While cranking to start, several things have to happen (assuming the engine is otherwise healthy and able to provide correct timing and compression). Primarily, the high pressure fuel system must meet minimum pressure, and the injector driver must command injector events.

Something as simple as a HP regulator or purge valve failure (for a variety of reasons) will prevent sufficient pressure to initialize an injector event. This can be easily seen with many/most scanners, including the simple, inexpensive "phone app" adapters. Connecting a scanner can also indicate the function of the computers. Missing values that should be present may indicate harness damage or failed computer modules. I'd start with checking the harness connections at the PCM and TCM, which are the easiest to access, and follow the harnesses checking for damage. A simple rodent intrusion could cause everything you've seen, which should be evident by their habits (nesting) and damage they do. I live in the sticks, and have visited this issue on several vehicles over the years, including a 2000 Impala that burned itself to the ground in my driveway, likely caused by rodent damage.