I have found that Pay-Per-Click advertising with search engines is a TOTAL waste of money.
I spent about $300 on PPC advertising with Google and Overture, and had a horrible outcome.
It's a sneaky form of competitive gambling. Unless you're one of the top 5 highest bidders (cost per click), you get no traffic. If you big high enough to be one of the top 5 bidders for any given term, you pay anywhere from $3 to $15 (for a measly CLICK!!). In the meantime, you have to compete and keep raising you bid price to outbid the competition.
Trust me, it's not worth your money.
John