For the hot water heater, call local plumbers. They can usually do it for less than an HVAC company. And yes, $700 is a good price. We had ours replaced some years ago now (I'm thinking 11-12?) - it wasn't leaking, but it was over 20 years old so we replaced it before we had to. I forget what we paid exactly, but it wasn't that expensive. We got a Ruud. We have had to replace the thermocouple twice now.

As for the clogged coil, you got off easy. We had the same thing happen last summer, to a furnace/ac unit in the attic. Water was leaking through the ceiling and started overnight while were we sleeping. So the next morning, we called the company that installed the furnace and had them come out that day. $800! And he was there for maybe 45 minutes! And my wife asked me the same question: Could I do that if it happened again? Damn right!