That... is a hell of a sale 0_0
It's actually probably an error, but even if it is, just buy it now. You get Tropico 4, alongside all of the DLC, expansions, and add on content... for $0.39.
So, er... buy it.
EDIT: And they fixed it, it's now $5.99, I think. Congratulations to those of you who nabbed it!