Write a native iOS app for socialengine.com or elgg.org like an already existing social application bud with reduced perimeter

We are a company doing IT consulting. We are looking for someone able to create a shortened by functionality native iOS app like an already existing social application downloadable from Appstore and Google Play As a backend we plan to use the engine from [login to view URL] At the same time if you have a sound experience with [login to view URL] or other known reliable custom social network engine solution either open source or or commercial , we would be glad to cooperate Main functions: registration with the device, geolocation check-in, sending messages between users, showing users on the map, search for a user by name and description Detailed budget is not defined yet, but we plan to avoid to exceed 500 USD Payment after a functional specification and perimeter negotiation, in separate transferts by each milestone achieved.