I picked up a portable cooler from Graingers a few years ago. It cost $110 at
the time and was the same model being sold by Charlie's Greenhouse supply.
Although these types of coolers do not work all that well on the east coast
because of the humidity it does manage to reduce the tempreture by about 15
degrees.

I install it in front of the screen door entrance to the greenhouse. The only
issue is having to fill the reservior since it does not have a direct
connection to a water source or a float valve but one could easily be
installed. It has a three speed fan and a pump to saturate the pad with water.
The reservior is made of plastic and after four years use there is only a
little rust on the outside corners of the metal at the base.