WebTimer

Description of WebTimer program from Softdepia.com:

WebTimer is software that saves you money by timing and/or restricting the useage of the PC. It can restrict not only the internet, but any software that you want to limit. If you use a MODEM to hook up to the internet, have a look at your most recent telephone bill and total up all the call costs to the internet over a one month period.

WebTimer is a "Free to try" program. You can download and try it for an evaluation period.