2001 Prius - dead battery with continuous horn

I really hope it's the fusible link and not the inverter. The 100A DC/DC fuse visually looks okay but the link could be blown somewhere else, right? I could maybe see spending $1K and installing it myself but spending $3K on a car I hardly drive these days seems a bit much. Since I had to replace three fuses already, I assume there's the possibility of another one somewhere I missed. I can see how hooking up the jumpstarter battery while the key was "ON" might have blown some fuses, but to take out the whole inverter? And would it be likely to go bad from just sitting around and not getting used for a month at a time?

Anyone know of a direct relationship between nothing coming on when the key is on ACC and the inverter being bad?