When someone does a search for a product or service they usually use Google and the they scan the first page of Google. Only 20% of people ever make it to page 2. 42% of people click on the first organic (free) link (only about 20% click on the ads). About 22% click on the second link. About 12% click on the third link. And so on down the page. If 100 people search for your product or service in your area and you're at the top you will get about 42 visitors. If your site looks good and engages them you will get calls and business. If 10% call you will get 4 calls. Compare this to having only 2 people come to your site - or worse yet, 0 people seeing your link on Google because it's on page 3 or worse. Compound this by having 5-10 keywords or phrases showing up on the first page of Google (and on other search engines as well) as opposed to 0. Where do you think the money is? I know where the money is. I know from personal experience because I do no other advertising for my business other than having a good website and doing SEO to rank well (and I'm in a very competitive field).
Next you should ask yourself what the average customer is worth to you in profit, over the lifetime of the customer. Ad in a little for referrals from that customer, and you get a better idea of what a customer is worth to you. Let's say a customer is worth $500. And being on the top of the first page of Google brings you 2 new customers a week. That's more than $4000 in profit per month.
SEO cost money, as does pay per click advertising. The good thing about SEO is once you reach the top, you don't have to do a lot to stay there, and so the cost drops, but the benefits remain. Good SEO will help you on all search engines. Pay per click benefits stop as soon as you stop paying.
What does SEO include? Onsite SEO should have been done on the site before it was taken live. Additional keywords can be added as they are determined. Links need to be built from other sites. Blog, forum and contextual link building is done. Social bookmarking needs to be done. Article submissions need to be done. Press releases are done. The list goes on in a comprehensive SEO campaign. Realize that a lot of work goes into getting you to the top.
I provide a comprehensive SEO campaign that is custom designed to get your site to the top of Google. You will watch it rise up the ranks. It takes a few months to get there, because that's the way Google works, and moving too quickly will look unnatural to Google and could cause more damage than good. That's why I use white hat techniques that will not get your site banned. Because it takes a few months for the best results you have to be willing to contract for a minimum of 4-6 months. Any less would be a waste of your time and money. More is better, but after 6 months you should be able to scale down or even drop the program for a while, although a small maintenance program would probably be best to fend off the competition.
The price would be determined by your budget and how aggressive you want to be. I ususally offer 3 packages based on certain criteria about your site.
I do not take on SEO clients that I think will not benefit from my services ( I want people to be happy with what I do for them). Feel free to contact me for a no obligation evaluation of your site.