Rep: It goes up by $5-10 every year after a promotion ends.
Wow. I never cease to be amazed by the land of free competition.
My ISP, Free, billed me 30 € ($39) in 2003 for 1mbps and no data cap. Over ten years later they still bill me 30 € ! Of course a lot has changed, there's still no data cap but the bandwidth cap has been removed too, I get unlimited phone calls to France but also about a 100 other countries including the US and Canada, and they provide me with a box which is an Adsl modem, network bridge/router (my choice), 4 port 100Mbps switch, CPL access point, WiFi access point, access to 4 milion WiFi hotspots, and a lot more.
They did increase prices once though: for a while I had TV over ADSL access for the same price but the government increased the VAT on all such offers so they turned the TV part into an extra 2 € option so that the VAT increase only applies to those 2 €.