I pay $70 a month for AT&T's gigabit (up/down) internet all fees, taxes, and modem included. DirecTVNow has intermittent buffering issues on my Roku TV/Roku sticks -- and I'm getting 200Mb u/d wireless from the location near my TVs and one of my Roku TVs is actually connected via Ethernet.
I didn't get the buffering issue when I switch over to my 3rd generation AppleTV over AirPlay. It's also not as bad on the 4th Gen ATV with the native app. If you get DirecTVNow, I suggest you take advantage of the free ATV 4K offer when you prepay for 3 months ($120). Even if you're not in the Apple ecosystem, you can still download the various streaming apps.