For online advertising for low cost and free I would recommend related forums, social networking sites, and article submissions for building backlinks to your pages. Also depending on what you are offering traffic exchanges can be good.
You asked a question made popular by newbies. You need to set some kind of realistic advertising budget. Keep in mind that you are running a business. The college campus idea has been effective for me also. I ran an ad in a Georgia tech student paper some years ago that had excellent results.
Of course you can always print well written flyers and hand them out around campus. Hang them at the student laundry center and on bulletin boards.
-before you choose which the best free tools to advertise it better to study your niche market.
then choose one or two of the free or low budget advertising tools such as :
* forums and most important related to your niche market.
* ezine advertising
* article submissions,
* social networking,
Attention: "role based name" email prefixes such as support, webmaster, info, contact, forum, service, affiliate, admin, traffic, partners, marketing, etc., for our member accounts are not permitted. They are acceptable for a vendor listing, but not for the member email. This is due to bulk email processors scrubbing them for delivery due to extremely high bounce rates. Please apply for membership using a personalized email prefix. Something like firstname.lastname@example.org.
If we discover you signed up with a role based name we will give you only one message to change it. After 3 days your account will be removed if the email is not changed.