Now you've gotten me to wondering. You were talking about "just one more" unit (Asus) as an option. That "implies" coverage is pretty good save for just one little weak/dead spot?
If so (and because I'm cheap) you could look at something like the Netgear 6150 (AC1200 range extender) with "fast lane". You dedicate one band as the "back-haul" to the router and dedicate the other band to serving clients. No wires needed about $80. Speed? Depending on how "bad" things are but 75 Mbps would be a reasonable guess.
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