Hi Juan Pablo Matarredona,
We have seen your attached application flow diagram & after discussion with you we can finalize the cost.
A very interesting concept to save money. With adding friends & creating groups. The ratings, notifications, & payment ( In app purchase) features to really help users to save there money with there family & friends.
We have 40+ skilled mobile apps & web development team, so please give few minutes for technical discussion of your requirement.
Dedicated resource with full time availability to your project with Skype & email reporting with prompt response.
Waiting for your reply & chance for further discussion.