A long time ago I was looking to buy an AGV Agostini replica helmet and in the same brochure AGV featured an air conditioned helmet but it required and auxiliary cooling pack. Right now there is a helmet MFG that makes a helmet with the cooling device integrated into the helmet. I don't find the cost of the helmet to be crazy expensive especially when Arai's cost 700 to 900 dollars. Take a look at the info here and see what you think.
https://www.visordown.com/news/product-news/air-conditioned-helmet-we-need-hot-weatherhttps://feherhelmets.com/