Generally where nobody wants to go. Which tends to be seasonal. In which case, I'm not sure if it'll help you, since I can't think of anyplace nobody wants to go at this time of year.

Ie, an obvious example is Phoenix in the summertime. But you have to wait months for those rates.

For the nonseasonal best chance, perhaps look for properties buried in business parks that are dead on the weekend. But I don't know if they'll be "absolute" cheapest, they may only be cheapest for that particular area or that particular brand.