He's doing so much better. I'm really happy. He's swimming around more so instead of hiding all the time. He now even approaches me and eats greedily. It's amazing what one day in some heated water can do.
I also have a potential local taker. She doesn't have a heater though but says she had a betta before. She's asking a lot of questions about what she should get if she can't afford a heater right now so that makes me hopeful that if she does decide to get him, she'll take good care of him. We'll see.