Popfax is perfect if you need to receive a large volume of faxes. For $63 for a year (or $24 for a 3-month term), you get 50 free pages and a new faxing number to replace your old fax line.
Each additional page faxed will cost $.06 and credits can be added in $6, $12, and $24 intervals.
If you only need to send faxes, the rates vary from $ 6 for 20 pages to $180 for 3,000 pages. A local number will cost you $3.75 a month and an option package (which will give you fax to email, call transfering, and voicemail, among other things, for $2.50 a month.