I plugged his numbers into a Numbers spreadsheet I use for estimating my taxes including self-employment tax. This should be the maximum that he would owe for 2013, though there is surely more that he can deduct.
It accounts for his wife and child, but does not take into account any personal deductions like mortgage interest, donations, or anything else. The state rate is approximately correct for Idaho where he lives though the state uses brackets below $10,000.
Just from the amount of deductible self-employment tax he's close to using itemized deductions, but would have to add more personal deductions to get to that point.
Business income: $256,725.00
Business expenses: $65,000.00
Self-employment tax amount: $19,233.48
Self-employment tax effective rate: 7.49%
Federal tax amount: $34,625.50
Federal tax effective rate: 13.49%
State tax amount: $12,463.45 (assuming flat rate of 7.4%)
Total tax amount: $66,321.43
Total tax effective rate: 28.38%