You need one of these plastic PA horns. They trade any hint of bass for a lot of efficiency. Even with 1 watt they are pretty loud, and without the bracket and crap you have plenty of weight left for a walkie-talkie board or BT speaker board. I'll bet a cheap FRS walkie would power it, and you could run that off your drone battery to save weight.

https://www.amazon.com/Pyle-PHSP4-6-Inch-Outdoor-Speaker/dp/B002UL0WEQ/

Oh and cheap chipamp (they have them even cheaper on ebay sometimes).

https://www.amazon.com/WINGONEER-TPA3116D2-Digital-Amplifier-Channel/dp/B01MG430H8/