$6 at Lowes, I have 4-5 of them. I sit them on a 30'' strip of 6'' heat tape so I have a steady supply of warm misting water. The seals go bad if you overpump it and not release the pressure.
Yeah i normally go through one or 2 a year like bt said. Always release the air when finished also will cause failure with the seal. I use the exact same ones lol. For my smaller mantids i still use the cheap hand sprayer though. That mister can really knock a nymph around.