This was a Google search and is taking in account for all types of graphic designers in general. No special industry.
The median annual wage for graphic designers was $44,150 in May 2012. The median wage is the wage at which half the workers in an occupation earned more than that amount and half earned less. The lowest 10 percent earned less than $26,250, and the top 10 percent earned more than $77,490.
This website has pulled averages based on specific advertised tee shirt artist positions.
http://www.simplyhired.com/salaries-k-t-shirt-graphic-design-jobs.html
