Nothing in this life comes free, but try the offering from CGISpy scripts. The way it works is that you set up a script on
their server that your visitors use (although they would never know) and this allows them (or not) access to pages in a protected directory. If you use the "Free" version your visitors get an advert, if you register for the service, which in my opinion is worth it, then there are no ads.
Have a look at their site for more useful hosted scrips. You just set it up and embed a text script that they give you directly into your static page and hey presto!
http://www.cgispy.com/scripts/password.shtml
By the way, I have no connection with this crowd except that of being a customer.
The down side to this scheme is that if a person knows the URL of your protected page then they can call it up directly unless your Web Host can make a private directory for you. Then you have the hassle of linking the password protection for that to the CGISpy thing. That is not impossible, and it works. However, it is important that you don't skip the CGI step as otherwise you will end up "hard coding" your password, either in HTML or JavaScript etc., for all to see if they investigate your page.
The trick with the CGI solution is that the verification and encryption takes place on a remote server to which the user has no access save the password input interface.