Bluetooth HID Pen Prototype

I want to prove that a pen-shaped gadget can masquerade as a Bluetooth HID and reliably control media on an iPhone. All I need right now is a working one-off prototype; certification, refined industrial design, and long-term battery optimisation can wait... (Budget: €250 - €750 EUR, Jobs: 3D Printing, Bluetooth, Bluetooth Low Energy (BLE), Electronics, Embedded Systems, iPhone, Mobile App Development, Prototyping)