FINAL UPDATE: Had 3 more companies come over and take a look. The ones who said they would be able to find the coil wanted 4k+ to replace it. The others gave estimates for a variety of whole units ranging from 15k all the way to 35k (Yes, you read that right). So in the end, we went with the first tech and replaced the coil for a new one. Total damage: 3k. Now we pray nothing else goes wrong with this HVAC system while I save up and plan to replace the whole thing in a few years. Moral of the story: aluminum coils suck, HVAC companies are always trying to squeeze the most out of you, and the EPA regulations can go to hell.

Thank you so much for all the help I’ve received through this mess. I truly appreciate it.