The out of warranty battery replacement, IF Apple Stores determine you have a failing battery issue and NOT other hardware/software problems is $99 U.S.D., plus tax.
Apple Stores do not repair iPads, nor replace batteries, but should offer you a refurbished iPad as a replacement, in lieu of the actual battery replacement.
This policy, it seems, is carried out on a store by store basis and by region and location basis.
Some regions of the world will actually send your iPad out to get a $99, plus tax, new battery installed.
To expedite quicker customer service, Apple Stores in other regions of the world may offer you a refurbished, replacement iPad for the cost of the $99 battery replacement.
You won't know the outcome until you take you iPad into an Apple Store for diagnosis and evaluation.
Best of Luck to You!