A lot of ISPs are public companies, so not sure why EFF didn't just dig up their 10-K filings?

Sonic.net is a pure broadband provider with pretty good introductory deals for 1Gbp internet in the Bay Area.[1]

2017 Revenue - $477M

2017 Net income - $64M

2017 Profit margin - 13%

13% isn't bad. It's more than low margin businesses, but doesn't seem egregious to me.

[1]https://www.last10k.com/sec-filings/sonc/0000868611-17-00005...