When you're running so low on money, the increased energy costs are potentially more of an issue than the hardware costs. You can often find cheap or free hardware, but if it is inefficient and increases your energy bills then that's more money coming out every month.

That being said, I've seen some people have success with using old Android phones as small servers. Probably can't do much, and not the most secure (as they will no longer get security updates) but definitely a low power option that should be easy to get hold of for free or very cheap.