Years ago I jokingly suggested to sell Crete to Turkey, in exchange for taking over Greece's debt (no doubt Turkey would jump at the opportunity and bend over to do anything possible to meet the debt payment criteria). The reactions I got were predictable, in the vein of "hell would freeze one hundred times over before this happens".

Jokes aside, selling territory (with actual sovereignty transfer, as opposed to simple real estate acquisition) seems to be a bit of no-go in the last decades. Especially selling it under duress for economical reasons.