I think you should definitely charge more. Here it is $35 for a yorkie groom (maltese, shih tzu),$41 for a poodle or Bichon, and like $40-something for a cocker. That includes a bath, cleaning out the ears, expressing the anal glands, nail trim, and groom. If they are matted, it's more. BTW - these are store grooming prices, not mobile. Mobile grooming prices are normally higher than store grooming because you are coming to them...and you're having to pay for gas.
Here is a link to a mobile pet grooming service in dallas, tx. you could always call them and ask for a few price quotes to get an idea of what other mobile groomers charge.
http://www.petlove.com/html/prices.html
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~Magnifique Yorkies~
Purchasing from backyard breeders, pet shops, and puppymills perpetuates the suffering of other dogs.
Educate yourself and buy from reputable breeders or rescue.