I would find a local nursery of even the big box for blueberries; they propagate fairly easily and are usually pretty cheap (my store charges 21.99 for a 4 yr, 3' plant in a 3 gallon pot). The big boxes are often less, but my opinion of the plant quality is for another time. Don't bother with mail order, you'll get a 1 year old plant that will take 3 years to bear for the same cost with the shipping.
Most varieties are going to be interchangable, some get bigger fruits, or sweeter fruits, but it's not really worth paying more for something. Just get 3 different varieties for good pollination and a lengthy harvest season. In 7b you should be able to do highbush or rabbiteye. I grow highbush in 6b with no problems except birds eating the berries before I do, might have to get some netting. And one stupid deer ate the flower buds on some last winter.
And a little secret: blueberries are incredibly beautiful plants ornamentally. Lovely white flowers in spring, flame red in the fall that is better than burning bush...use them in your landscaping. I planted mine right in my front flower beds under the bay window, they look great. Well, they did before yesterday's 18" of snow buried them.