Is it your first one? I would suggest taking a very reduced rate.. to almost approach it as an internship and get some a good track record under your belt. Once you've done it you will learn better how to factor time estimations and budgets, then in turn, set a dollar amount for estimated work load.
price of your service must depend on 1.Quality of your service 2.time duration for complete the order 3.your knowledge for particular service (like. directory submission) it doesn't matter your price is higher or lower than other, but high price means your effort is higher than other For base price you should visit some of seo service provider website
If you have any fixed budget, then you would obviously not take anyone's advice. But if you don't have a fixed budget, then Request quotes / proposals from at least three seo services and take a call with all the three. See who's proposal is more convincing and professional, then take a track record of their success etc., go for the service which you feel can do a good job. TIP: Most of the seo services promise which are impractical... eliminate them.
One thing I will suggest is take overlook at your nearest competitor's rates and proposals and then according to that you can get idea.