Miniaturize Motion Sensor Prototype

I need an existing motion sensor prototype miniaturized to a 2.5x1.5x0.8 inch package. Requirements: - Reduce size of circuit board, casing, and power supply as needed - Maintain functionality and performance... (Budget: $250 - $750 USD, Jobs: Circuit Board Layout, Circuit Design, Electrical Engineering, Electronics, Embedded Systems, PCB Layout, Product Design, Prototyping)