The most inexpensive kit we carry is going to be the Boulder Rock. This excellent starter kit is only $12.99. While nearly every device we carry is going to use "coils" that need to be changed, the Boulder uses pods that can be easily switched out when necessary. These pods cost $7.00 for two of them, making them $3.50 per pod. The battery life will differ based on usage. These are available in the color black. Liquid consumption is next to nothing thanks to the amount of power being used in the device. Not only is the device inexpensive to buy but also inexpensive to upkeep as well.