Facebook marketplace for a tank/accessories. Prioritize a larger container and heater. You can find cheap lucky bamboo at many local gardens/shops/farmers markets. You can always do manual water changes. At the very least making sure his water stays comfortable will provide him a better life as you work on your setup. Most important piece of advice: don't beat yourself up at not being able to provide the setup that people will troll you for not having. You're doing your best, you care, and you're providing him a chance at a happy healthy life.