We just confirmed with Apple that swapping out the 17" MacBook Pro's non-removable battery will cost $179. Fortunately, says Apple, the swap might not be needed for a long time:
From a spokesperson at Apple:
It will likely be years before you need to replace it (1000 cycles at 200 cycles/year = 5 years). You can have the battery replaced at any Apple Store or Apple-authorized reseller. The replacement battery is priced at $179, which includes installation of the new battery and environmentally-responsible disposal of the old battery.
The non-removable MacBook Air battery costs $129 to replace, though the lifespan is not promised to be as great. [Apple]