The GPS is built into the same circuity for the Cell transceiver. There is no requirement to ever activate the cell service but the iPad with that extra circuit costs $100 more up-front. So let's say you buy a separate Bluetooth GPS, that will set you back at least $60 (plus shipping or tax) and so the net difference is about $40 maybe less. So for the extra $40 you've got one neater package, less fuss for setup and only one device to charge (or not).

As for battery, that's really not an issue. I find the iPads very power-efficient with or without the GPS. I already owned a Bluetooth GPS when I bought the iPad and still got the model with GPS so I wouldn't have to fiddle with it.