how do I advertise my website without spending much money?

[Rus]

If you are going to advertise, it's going to be pricey whether you buy banner ads, AdSense or TV commercials. With AdSense you could set the limit on your expense but then you also limit the effectiveness of your effort.

As others suggested, in addition to advertising, you could make an effort to improve your website position among search engines' result, the process known as search engine optimization or SEO. It has advantages of being free or inexpensive and it could be more effective then advertising. People naturally distrust ads, but when a website appears among the search results, there are less reservations.

There are several things you can do and they are free or near-free.
Build you site in a way that is friendly to the search engines. Read the article that I link below for guidelines
Generate buzz and links to your site. For that you are going to need to write articles, blogs and to use social media.
Create accounts for your site on facebook, twitter and others. Get people to follow those accounts. Post frequent news and updates.
Create blog accounts on free sites like blogger and livejournal and start blogging about your site or product or service or whatever. In addition, you could sign up for blogging service like v6transition which has some specific advantages for your marketing efforts.
As you blog, be sure to include links to the pages on your site. That is how your site's position in the search engines improves.
Be careful not to over do it, both the number of blog postings and the amount of links in them because otherwise your site could be penalized by the search engines. A dedicated blogging platform could prove advantageous in preventing you from harming your site.
Finally, you could write articles (free) or press releases (not free). Just make sure to thoroughly proof read and spell check them.
Good luck