A variable power supply, or use a 10 cent (if you buy 50 on Amazon) 78L05 voltage regulator plus a 10 nF capacitor from the input to ground and output to ground (2 cents each as part of a 300-piece assortment) with either a battery or wall wart.
https://www.amazon.com/dp/B075CY7VFD https://www.amazon.com/dp/B084VMLSFQ