First question how far are you from a tap, second question is it outside, the tap I mean, and third question are you away from your green house for long periods.
I irrigate my large greenhouse with watering cans and buckets, two buckets and three watering cans will give enough water for a week, I fill them carry them in and leave them using as needed.
I have a watering system that is used for when on holiday or away for a while, it cost £35 at B&Q and is a hose pipe with a drip feed system one feed goes to each pot and the hose is carefully set to give a steady drip. When I am away the door and windows are left open, it is better to be cool than overheat the plants.
A greenhouse with plants needs at least twice a day visitations to adjust air flow open and close vents as required being retired and working in the garden I do keep a constant eye on things and lose very little from cold heat over watering, the three main issues with greenhouses.
I find the irrigation system can be fickle at times, can lead to some plants being over watered and others left dry so it only comes out when I am desperate.
OK probably not what you wish to hear but I Can only tell it as I find it, a misting system as used by commercial growers costs the earth and we pay for it buying their plants.
Frank.