Needing to leave, caretaker backed out..

[Tortoise]

Wow, so sorry, tuff situation. If you have dog walking businesses or individuals, sometimes they take on other animal care jobs too. You might look there if all else fails.
I don't have chickens yet, so no experience with the different waterer s and keeping them thawed for cold weather. However, instead of a 5 gallon bucket how about using a large black plastic garbage can? It would much more water and could still use the heater. Maybe even wrap the outside of the can with insulation to help prevent freezing.
Good luck. I think it's great your willing to spend this time with your uncle.

 

[WannaBeHillBilly]

I don't know when you have to leave, but there may be a little time to DIY something.
Facing a similar problem with my ducks: Having a cr@ppy job which forces me to leave home for days, a muddy yard, bad cell phone coverage and a wife that i don't want to find injured in the yard (or worse) when i come back home, i am currently building a maintenance free duck-waterer. This is the idea:

I have the PVC pipe cut-out, installed the float valve and the drain-pipe, i don't know exactly how to fit in the pipe-heater cable and i need something to hold the pipe and lift it from the ground. With chickens, you may be able to leave the drain-pipe out of the picture, my idea was to let it drip (therefore the valve), so that the food-muck that the duck produce will be washed out permanently.
The float-valve with garden-hose adapter was $13 on eBay, the pipe heating cable was $17, also on eBay. The valve was $6 at the hardware store, the knee was $2, the pipes were left here by the previous property owner. A bit elbow grease and your birds have a free drink day & night.
This is where i am at the moment:
The float-valve assembly and the cut-out pipe
The float valve installation
The drainage hole with the knee screwed in
This is how it looks from outside
everything together
I hope that helps.