Prototype Wearable Contactless Payment Device

I need a working proof-of-concept: a compact wearable that accepts payments from my proprietary contactless card and houses a SIM-enabled module to forward each transaction. The balance must live on the... (Budget: $30 - $250 USD, Jobs: API Development, Electrical Engineering, Electronics, Embedded Systems, Firmware Development, Microcontroller, Payment Processing, PCB Layout)