Thanks for the reply.
If you are arrested, in Wisconsin a theft offense involving $438 would be a class A misdemeanor. You can see what the state would have to prove against you here in section 943.20 of your law.. The maximum penalty for this crime would be 9 months of incarceration and/or $10,000. In practice, however, although the statute would allow for jail and a very hefty fine, the odds of you going to jail are just about zero. If the police believed you belonged in jail, they'd have taken you in after they spent 2 hours with you.
If you are charged, you should have a lawyer with you when you are in court. You have a mistake defense and didn't have the intent to steal, so you may want to fight this case. In any event, if you can't afford to have a lawyer with you if/when you have to appear, you can just plead NOT GUILTY when arraigned on the charges. If you're living on disability, you would likely be able to qualify for a free lawyer. So after you plead not guilty, you can tell the judge you cannot afford a lawyer and ask him to appoint you a public defender.
Since the police left without charging you, this may be something that the police and the state won't want to prosecute. They may tell your neighbor to sue you in small claims court for the money instead. On the other hand you could still receive a citation or a summons and have to deal with the charge in criminal court.
I don't know what you want to know about this situation, so if I didn't touch on the aspect you were hoping to learn, just reply to me here on this question thread and tell me and I'll be happy to add to my answer.