The best way to find out is either to look what other people are charging or even better work for someone as a protege or apprentice.
rates will depend on the country you are living in and even then many companies outsource the work, bringing down the expected rates, then consider what result they want and how competitive the market is a highly competitive mkt will take more work to get the conversion than another market where competition is not so competitive
The SEO pricing is dependent upon the quality of service you provide. Just by copying the prices of the competitors, you cannot give the BEST.