Clouds on stage: Seeking advice from techs

The cheapest way is with a low fog machine such as the Antari Ice but with any of these machines which are smoke machines with an ice bucket to chill the smoke and special dense smoke, the effect only lasts for a few minutes. So you could use these to set the atmosphere for the start and end of each scene and let your lighting keep the illusion during the scene. As others have said, there is moisture and condensation with these units and any draft plays havoc with the low fog. The low fog tends to roll off the stage into the audience which is not desirable. If you have raked seating then you set up a low barrier. If you want the effect to occur during the scene then the parachute silk would be the way to go. The hazer is designed to sit in the air so would not be low enough if you were standing on the clouds.