IBCLC certification is the way to go. It stands for International Board Certified Lactation Consultant. It's initials that you put after your name, just like an RN or MD, etc.
There are many different paths you can take to get cert. - more or less contact hours depending on how much education you already have. Most IBCLCs get their RN first, but not all.
Financially- I recently hired an IBCLC privately to visit my home after the birth of my daughter (now 2.5 months old) and she charged $100/hr. with a standard 2 hour visit. She charges $35 for travel if it is beyond a certain mileage and $15 for an initial phone consult. I'm sure that there is somewhat of an initial investment (beyond paying for your education and for board exams, etc) because she had various supplies with her as well. These included a scale to weigh baby before and after feedings, dental syringes (for when baby needs to be bottle fed but won't take nipple), documents to keep records for herself and for me/insurance company, probably nipple shields, etc.
Joining online groups of others in the birthing industry can help too. I have learned quite a bit by joining a yahoo group of doulas and other IBCLCs, etc. and by hanging out on forums where there are other nursing moms and just observing their issues, etc.
Hope this helps! As you can see, I'm wanting to become an IBCLC myself, and have for 7 yrs now, but am waiting until my children are a bit older before I go back to school or work.
Amanda R.
aspiring IBCLC