As @msinger mentioned above, the extra battery combos include an extra battery for an additional $100. We expect individual batteries to be priced between $120-140 so you going with the extra battery combo will save you an Andrew Jackson or two
You will not see pricing other than the $1099 for the Advanced with Extra Battery or $1359 for the Professional with Extra Battery. These are the DJI MAP prices and Authorized DJI Dealers cannot sell below these prices. Any seller posting below these prices is not an authorized dealer and you would not have a valid warranty should any problem arise.