Last I heard, the national average fee per taxpayer was $285. Highest fees are charged in big cities on the coasts. I'm in a small community in the middle of the country and my average per taxpayer last year was $283.
Tax returns that are genuinely "simple" are usually self-prepared by the taxpayers. Why do they need a professional preparer? You want the situations that are not simple -- such as people with lots of tax credits. The preparer due diligence for the Earned Income Tax Credit is so detailed that you should charge at least $150 for those returns. Charge over $200 if they itemize deductions and have other tax credits. You can sell this price based upon your calculations giving them a greater tax benefit than your fee.
Even better are people with business interests, investment income, or rental properties. Promote your ability to accurately handle those circumstances. You might have better success by passing the Enrolled Agent exam and marketing an EA designation. Based upon your experience, you only need a good exam review course like fastforwardacademy.com/enrolled-agent-exam-prep.htm. Point out to your clients that people doing their own calculations on these matters result in the 200 million IRS notices generated annually. Taxpayers who use Enrolled Agents avoid that trouble.