A June 1997 report from the General Accounting Office provides a treasure-trove of information about the cost and the scope of online resources made available by the executive branch of the federal government.
It also includes a list of 4,300 federal Web sites. (See below.)
The report, reproduced here on washingtonpost.com, contains several useful sections.
Read the introduction, the results in brief, background on the Internet and electronic bulletin boards, and a table showing estimated expenditures by agency for 1994-96.