I need help with the SEO pricing

Is it too much to charge $3,000 for building a Shopify store (websites as huge as having an entire ingredient directory, 500+ pages) and then another $1,200 a month for SEO? I have had great success with organically growing Shopify store and boosting sales as much as 465% in 7 months while ranking several of my clients' store on the first page (over time) for some keywords with 3x - 5x traffic. I have seen agencies charging $10,000+ for the same. Is it really too much to ask even after having successful results to prove? Another question to Shopify owners - What is the maximum you have/are willing to spend on an SEO service? Any advice would be great. Thanks in Advance.