I use Sling tv blue package with an OTA antenna attached. When it comes football season I add the orange package for ESPN games... and then drop the orange after the regular season is over. If a Bills game isn't on either of those I have to go hit a trusty online place.
However, the NFL app shows a lot of games you can watch, depending on your location.
If you have a chromebook you can download the app and watch on a decent sized screen. Might be a smaller screen than you would like but its better to watch Bills football than not watch at all. You can always pipe it into your regular tv with a cable.
I know a couple of people that use a superbox... google it... they have never missed a Bills game and it is legal.
Google superbox... that's all I've got for watching Bills football.