HiDow XPDS 18

My wife bought a HiDow XPDS 18, about the size of your hand and weighing only a few ounces, which uses Transcutaneous Electrical Nerve Stimulation (TENS) and Electrical Muscle Stimulation (EMS) technology to help relieve sore, stiff or aching muscles.  I like it on my lower back, hamstrings and feet, and it really helps.  She scored ours at a local tennis tournament for half the list price you'll find on this website, and I've seen used models on eBay for as little as $100.  They make a number of models with different features at various price points, so shop and compare to get what's best for you.

https://www.hidow.com