When commercial greenhouses are set up, they install huge fans. To keep a greenhouse cool on a 80 F day, you need to be able to exhaust the entire volume of the greenhouse at least once every 3 minutes to once a minute. On a hot day, you need to move a lot of air. As the temperature goes up, you need to move more air. On a 95 F day you would need a complete air change once a minute to keep the plants from getting hotter than air temperature.
You need to break out your calculator. Calculate the volume of the greenhouse. Then shop fans at a place like Greenhouse Mega Store. Look at the volume per minute values for the fans. ANother place to shop is Grainger.
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Hobby size greenhouses are usually intended to keep plants warm in winter, and are usually empty for the summer, everything being put outside. They are not normally built with enough ventilation for summer time use. If you add ventilation, they can be used year round.
Swamp pad coolers are economical for cooling a greenhouse, if humidity is not too high during your warm spells. Swamp coolers work by forcing air through a fiber pad that has water dripping through the pad. The water evaporates, chilling the air as it evaporates. Works really well as long as the relative humidity is less than 90%. During very humid weather, the cooler will not work. Probably no problem in your state. In places like Louisiana swamp coolers are not as effective because of the high humidity outdoors. In the desert southwest they are very effective, though the amount of water required is somewhat scarce and expensive.
For protection against critters. Instead of a glazed greenhouse, a screenhouse might be a better option. Essentially replace all the glass with wire mesh. If your glass or plastic panels can be removed without damaging them or the frame. Consider removing panels and replacing them with wire mesh or window screen. Replace the glazing as weather cools in autumn. Or have 2 structures. A greenhouse to extend the seasons, and a screen house for summer time use.