The only information available so far suggests the expansion will arrive this summer and will be first available exclusively on the Xbox 360. Other gaming consoles (PlayStation 3 and PC) will get it a month later, according to Eurogamer. Bethesda did not announce any sort of pricing scheme.
Looking at the teaser image, everything seems standard about the picture of Dragonborn except his eyes. In the original Skyrim images issued to the press, those eyes usually don't glow like that, so maybe the protagonist gains a fiery infusion of power.