07 Tahoe LTZ fuse box fire



I have a 2007 Tahoe LTZ that almost caught fire in the parking lot at work! Went out to my vehicle at lunch started the vehicle for approximately 5 minutes turned it off, no problems. About 20 minutes later started the vehicle again and it hesitated as if the battery was weak. Only ran it for about 2 minutes. Just out of curiosity, tried to crank the vehicle again no start. Radio, lights, gauges, electrical windows worked. Even locked my vehicle with the key fob. Did not smell ANYTHING when I left my vehicle and went back into work.
When I got off of work about 3 hours later, I could smell "electrical wire" burning smell about 6 ft from my vehicle.
Key fob did not work. Engine would not turn over battery completely dead, no power to anything.
Attempted to jumpstart the vehicle, it would turn over but no start. Gauges radio lights would work while hooked up to another vehicle.
Took a look in the fuse box to figure out where this burning smell was coming from. Please see attached photos!
Was going to replace the fuses, but whatever caused The attempted fire or whatever it was evidently had something to do with the alternator because it is fried!

Had it towed to a shop and they are wanting to charge me a minimum of $1,400 just to replace the alternator in the fuse junction box. THAT IS NOT EVEN DIAGNOSING WHAT CAUSED ALL OF THIS IN THE FIRST PLACE!

ANY IDEAS ON WHAT I COULD HAVE CAUSED THIS TO HAPPEN?
vehicle had been running and idling rough for about 2 weeks. I did smell gas in the cabin so thought it could be a potential misfire on a cylinder??
I don't see spending a minimum of 1400 dollars without a diagnosis of what caused the problem on a vehicle that needs other repairs!
I need upper and lower ball joints, shocks and struts.

Any thoughts would be appreciated!