When it comes to your SEO there are 2 options-
Option #1 is to tackle it yourself! You are going to need a computer with an internet connection, ability to make website changes and some basic computer skills such as how to cut, paste, copy, email and microsoft programs.
Next you will need a presence on other high ranking websites. You will have to set it up and then give it daily attention.
Option #2 subcontract your SEO out. This is great option for more competitive keywords and if your time is limited. You pay a monthly fee and and everything is done for you.
The cost is determined by the competition of the search terms and if they are local or national.
Not only is SEO a better return on investment than pay-per-click it is far further reaching.
You can never get back the time you wait, to invest in yourself.