Lifeproof FRE "power" cases are more expensive than regular Lifeproof FRE cases because they offer the ability to recharge your phone without a power cord. The extra battery is in the case. If you're looking for just a waterproof case without the extra battery, you can save money.
LifeProof - NÜÜD Protective Waterproof Case for Apple® iPhone® 6s - Cliff dive blue
(118)
LifeProof - FRE Case for Apple® iPhone® 6 and 6s - Pink
(727)