>>At 27% humidity, a swamp cooler would provide great cooling, for very little money.
Bump that.
Throw in a whole house fan to circulate the moisture molecules on a path through the house sucking heat as they go... to be expelled out the attic vents.
Thermostatically controlled Fans on the attic vents also help.
Swamp Cooler without circulation = a humid, moldy, hot, mess.
Ahhh, we used to have a whole house attic fan at our old house. It might’ve been a tad on the loud side, but boy, did it do its job! In this house, we have rarely had the need for such a thing. Our lot is full of mature trees that hover over the house. God has provided for us naturally.
A liquid desiccant based cooling system could operate well in a high sun area. For an arid region, recovery and reuse of the water coolant would be a consideration.
http://ailr.com/liquid-desiccant/ld-tutorial/