The suggestion by Steingrimur is probably the way to go. However, there are also low-cost alternatives. Please check the paper in the attachment if you want to know more.
Regards, Christian
Article Removal of dodecyl sulfate from protein solution
Cf.: A. Alam, "Agent for protein precipitation, a method of protein precipitation, a method of protein assay using protein precipitation agent, and a kit for protein assay", US Pat. 6,875,617 B2; Apr. 5, 2005.