This single-layer board is easy to produce and a cheap-cost EMG module that would let you peek into muscle tracking. The module should be connected to any analog pin of an Arduino or similar board. NOTE that GND on the module should be connected to Arduino's GND. Electrodes should be bought separately. I would recommend Amazon as the easiest source. You need electrodes with a 3.5 mm mini jack. The total cost should be less than 30$ without electrodes. PCB can be produced by basically any DIY method as traces are wide enough and only through-hole components have been used. R1 and R2 are used to set the gain so you might want to place the pot at first to determine the perfect values for your application