The industry standard for mastering is 200 dollars per song. The top engineers charge 400, but you can count the number of people that can stay in business with those prices on one hand. They more or less have perennial invitations to the Grammies.
I charge 25 dollars per song. And I can promise you that what I offer can be fairly assessed to be 90% of what you would get from someone charging 200-400 dollars. I may not have the Pyramix rig, the Prism Blue converters, the Ampex 2'' tape machine, or the DunTech soffit mounted speakers. But I learned from some of the best, and my ears are very well trained. And I'm charging 12.5%.
I'm doing this for the DIY'ers that are the world's best hope for great, new music. The people who want to put out great demos, EP,s and Albums without having to spend all of their money. And that's exciting.
If you have any friends that may be interested in my services, please spread the word. Like on Facebook. Follow on Twitter. Blah Blah Blah.