SEO is a long time job. And your keywords rank higher for a long time.

SEO involves many techniques like link building, directory submission, comments, articles, blogging, ads etc. Thats why it is expensive.

ya, it has very popular.

Yes you are right..

SEO cost is depends upon the business. if u want to immediate business then u can do ppc otherwise SEO is best....

If you cannot afford a seo then you can start learning seo and apply on your site then it will be very good to you and your site where as time matters because spending lots of time like dedicating your complete time in learning and applying may not work always that is why people will choose seo professionals and the term expensive will only suits to the ethical and professionals who has already proved and in a race where no one can be there this is why some professionals coast may be differ according to their standards. and if you want instant traffic then you can go with ppc like programs other wise it is always a good thing to practice seo strategies.

Search Engine Optimization is broadly divided into two parts. On Site Optimization Techniques like Title Optimization, URL rewriting etc and stuff that you do on your site. Off Site Optimization Techniques which would be done off page, that is not directly on your site. Like link building.