GPS systems much like the Magellan Road - Mate 5045 and the Garmin Nuvi 1300 cost lower than $100 and have a surprisingly full group of features. It is well suited for tracking any person with diminished mental capacity and even monitor the teen drivers in your family.
It offers a sufficient volume of features due to the price range. At each price level Garmin offers models which are waterproof or ultra-thin.