The tax will be whatever it is no matter what structure you use. For example, you could make a consulting corporation and pay yourself and your wife salaries and issue W-2s. The corporation might show no taxable profit and all the income will go to you on your personal tax returns, where your net tax would be about the same, just with more paperwork for the corporation.
If you are "middle class", married filing jointly and make (let's say) $75,000; the first $75,000 is taxed at a blended rate that will average about 13%. But every new dollar you bring in will be taxed at 25% federal. Every dollar you bring in period is taxed at 15% for social security and medicare, when you are an employee, you pay 7.5% and the employer pays 7.5% (and that probably holds gross wages down); when you are self employed you pay both shares for a total of 15%.
If you make less than $74,000 combined then the estimated tax on new dollars earned may only need to be 30% (15% federal plus 15% self employment).
