For building a vertical wind-powered turbine system, suggestions for small, affordable generators include using 12-volt DC motors from vehicles, such as those for windshield wipers or windows, which can function as generators in reverse. It's important to consider that most vertical axis windmills operate at high torque and low speed, requiring proper gearing to achieve higher RPMs for effective energy generation. Homemade generators using Volvo wheel hubs and custom-wound coils are also recommended for those looking for a DIY approach. The target specifications for the generator are under one foot in diameter and priced below $50, with a power output of 1 kW or less for optimal performance at airspeeds under 15 mph. Overall, careful selection and modification of components are crucial for building an efficient wind turbine system.