I think it was 1995 when WOW!, which was a subsidiary of CompuServe, offered unlimited hours for $15/month. AOL followed shortly thereafter. Prior to that it was something like $4-6/hour, usually at only 14.4kbps - 28.8kbps.
Going from 2.5 - 4 hours a month to a household being able to easily surpass 100 hours a month (for households with multiple kids, easily 150-200 hours a month!) was an absolute game changer for internet adoption, at least in the United States. Then add in Mosaic (eventually Netscape Navigator) taking off and that's when adoption really ramped up. Then cable modems and DSL starting to become more widely available in 1997-1998. Plus instant messaging software basically being the precursor to what we would see later on with SMS.