Exhaust fans won't really help if you have sides rolled up. They will just draw air from the nearest opening. But if you don't already have exhaust fans and intake louvers I would suggest them for Spring and Fall ventilation.

I don't believe a ridge vent is a good answer either. They not only cost a lot but they complicate the simplicity of the high tunnel. Consider the potential for additional heat loss if the seal isn't tight; replacing film is much more labor intensive; there is more to malfunction and more to repair.

I do recommend circulation fans to move air within the tunnel and a shade cloth to block some of sun and thereby cool the interior. I can't tell you that midday will be comfortable in the tunnel no matter what you decide but the shade cloth will help a lot. The circulation fans are mainly for the plants- disease prevention, pollination, and elimination of cold/hot spots.