Just to give you a ballpark figure on Google advertising....
A featured ad which is on the top highlighted box on the search result page start at $15,000 which the campaign last for three months, and that is the starting price.
Google is a great bang for your buck, but also remember that your website has to portray what you are selling in under 10 seconds. People do not want to investigate what you site is about, but rather know what it is about by the first glance.
Also, your ad words on Google marketing has to be right to the point but make someone want to click to hear the full story within 10 seconds on your site.
Keep it easy, professional, and do not be vast on the product(s) that you are selling. If your site has to many categories, I just suggest making a different site for them and keep focused on the product(s) at hand.
Thanks and good luck!