What is the best on-line fax service availble for the cost? Is it possible to add this to my website?

Answer 1

eFax received PC Magazine's Editor's Choice, but you may want to look at their reviews of some others.
http://www.pcmag.com/category2/0,1874,1841636,00.asp

As for adding it to your website, if I understand what you're asking, you should be able to put the email address for your fax account on your website.