One of the building block projects I”m working on is a small boost regulator that can take a coin cell or two AAA’s and boost the voltage to 5V (or 3V with a part swap) for use with an AVR or Attiny (or your favorite mcu).
The NCP1402 series of boost regulator’s costs about $0.72 in single quantity. The NCP1402SN50T1G I’m using can take a voltage as low as 1.8V and boost it to 5V at up to 200ma. The NCP1402 is a smd. This project also gives me an excuse to try using a new service from Digistump called pcbs.io. The photos below are prototype boards from pcbs.io