I used a couple of these: https://www.tp-link.com/us/business-networking/antenna-and-accessory/tl-ant2424b/ https://www.tp-link.com/us/business-networking/anten

I used a couple of these: https://www.tp-link.com/us/business-networking/antenna-and-accessory/tl-ant2424b/ https://www.tp-link.com/us/business-networking/antenna-and-a... And 2 cheap Asus routers for 400 meters. Would've likely worked for twice that distance. Iirc the total cost was less than 200 Euros. Pretty cheap and easy, too.