Rescuing a fungusy dahlia

I didn't buy the $2 box (they have some at the grocery store). I paid $9 for 3 bulbs at home depot while they were fresh, planted in the greenhouse and didn't water. A hailstorm did water on march 23rd when it took out the greenhouse roof but by that time they were all up and looking good. The smallest one started looking wilty 3 or 4 days ago, so I removed it from its damp pot, moved it to dry potting mix with the bulb coated with cinnamon, and watered it with some peroxide, not much either. Mostly dry soil. Not dead but not improving, today I dug it up, trimmed the rotten ends off a couple of bulbs, poured some peroxide on it then coated it with dusting sulfur and got on here. Considering dunking it in bleach water, recoating with cinnamon and sticking it in rice. HELP. I am thinking nothing can save a dahlia once it gets fungus.

I think I'm rinsing it off and taking it back to home depot in the morning with my receipt. don't know if the other 2 are infected but I just googled symptoms and this could be a virus? but the bulb was soft and mushy. If there is anything I can do for it feel free to let me know. I didn't even put these IN the ground around here.