This was the question asked by a client to me while we were talking about an seo project . Here are some of the factors which decides the pricing

1 . Competition of Keyword : Definitely the keyword is the first and foremost in the case of pricing an seo project .As the competition of keyword increases , the pricing and time for completion increases .

Example : Consider a company in kerala(A place in India) proving services to its clients in kerala only . The keywords will be related to “kerala+service name”  most probably this will be so easy to attain. And may be acieved within 2 weeks or so .

Consider anther general keyword like “buy mobile ” , “hotels india” , these all are highly competitive keywords with thousands of searches a day . Achieving top 10 rankings for these competitive keywords will take much more time,careful study  and hard work  .

2 . Competetors : Find who else are trying to acieve ranking for the same keywords. If they are also working hard , the work wont be easier .

3. Current ranking of the website to be optimised: The current ranking of the website is an importanat factor in the case of SEO . If the site is new and having no ranking at the time of start , the work will be more. And if the site is old and have some nice rankings already , then the work will be relatively easy .

4 . Geography of the userbase : As the geographic location of the client chages, the difficulty and pricing changes .