tc, If the plumber solved the odor problem and eliminated the irritating gurgling noise in the tub, then I would say that you received good service at a fair price. Consider the cost of doing business in the Plumbing trade today, and the cost of the equipment, tools, and training the Plumber must acquire and maintain. Believe me, the Plumber had a lot more than 40 minutes invested in that job.
John Aldrich (Septic Tank Yank)
Septic System Consultant (Not A Plumber)
Timnath, Colorado USA