Hello, I'm an Android developer with years of experience in mobile apps. I'm currently working for a major UK mobile development company, based in Colombia. I'm interested in working with you, and due to the simplicity of your idea, I believe it can be completed in the time proposed. I would like to discuss the details of the app with you, in order to have a better understanding of what you want.
Looking forward to hearing from you.
Best regards,
David.