Based on posts here on FT, having a prepaid reservation doesn't seem to make any difference when they run out of cars. I've never even heard of putting down a deposit otherwise, I see no way to do that on their web site reservation pages.

At the very, very least, Hertz should refund the one-way charge, and they should really refund all of the out of pocket costs. Getting them to do that is another matter. I'm not sure if it will help with Hertz, but a lot of people have found that Twitter gets faster responses with various airlines, hotels, etc., you might want to try that.

And if nothing else, you can see Seinfeld's take on this situation.: