5GHz WiFi is not line of sight only, the signal does travel through obstacles. I personally had an RT-AC86U router before and my backup router now is C2300. In my place both can reach 2 rooms away from the router (>10m distance) through 2 walls on the way (1 concrete + 1 drywall), in both 2.4GHz and 5GHz bands. Routers based on BCM4365(6)E radios currently offer one of the best AC WiFi performance. Again, if one of those can't do the job, then you definitely need more than one APs. The best WiFi coverage AC router is probably Netgear R7800, but it's above your budget and it's just a bit better then similar class products, not like "Wow!" of a difference.
RT-AC86U has more frequent firmware updates compared to Archer C2300, the firmware offers more options, it's the more popular router. This forum offers great community support for it. The reliability rating is not as good as previous ASUS routers, but it's covered by ASUS warranty. There is an still unresolved intermittent software reboot bug, but simple rower cycling the power button is all that's needed. It happens rarely, you may not even see it, some people don't even know about it. Just avoid remote updating/rebooting of this router. Get one from Amazon (it's currently on sale), see what it can do in your place, if it doesn't work as expected send it back.