Certainly conventional cable TV has involved paying for channels with ads at least back to when I first saw cable TV. However, the percentage of time for ads keeps increasing, and the prices keep going up.
But a quick check at an inflation calculator makes me question whether they are going up faster than inflation. For example, I think our cable TV bill in the early 70s was in the teens, and an inflation calculator says that $13 in 1973 is about $98 now. And that was for about 18 analog SD channels with commercials, one cable box, no DVR, no remote even.
There are more ads per hour now, however the number of ads actually watched per hour is probably at least 80% lower due to DVRs. This presents a bit of a vicious cycle for those who don't skip the ads because they have to make up for the rest of us.