As a poor man's option, what do you think if I just got the Tenda AC15 and keeping the modem that I have? I just need the wifi to be at least twice as fast; my wired connection at 140 mbps is honestly good enough for my needs (I typically don't have more than one device connected to the wifi at a time).

Did the price go up to 70 recently? I'm looking at this one right now https://www.amazon.com/Tenda-AC15-Wireless-AC1900-1300Mbps-External/dp/B0143HBZMW