The strech goal wasn't met, so only the $750 tier and above will get a 64-core board, so I would suspect that once the parallela is generally availabile, the 64 core version will be significantely more expensive than the 16 core version.
My understanding (which might be wrong, so anyone from adapteva correct me if it is , is that the 64 core version needs to go through the same kind of "retooling" than the 16 core version to bring down manufacturing cost, get more chips per wafer.