This work presents an open design for a low-cost (100 USD) MR-compatible force sensor to be used in the context of dynamic muscle MRI/MRS. The sensor is both based on commercial nonmagnetic components and custom manufactured parts. The electronics is realized using Arduino and a prototype software interface is presented. The sensor is calibrated using a commercial dynamometer and shows good linearity in the sensitivity. The setup is proven to function in an MR environment without disturbing the signal acquisition.