You are embarking on a whole new career path! While it may not be as costly or as time consuming as obtaining a four year degree in education, for example, it does require time, energy, money, and commitment. There is the tuition for your lactation education program -- a week long course may involve airfare to the city where it is being held, hotel, and meal costs. You still need another 45 hours of lactation education which may involve conferences or the cost of home study.
You will need up to date lactation texts. If you need the college and continuing education courses, there is the cost of those. You may need to work with an experienced IBCLC to mentor you while you obtain your clinical hours, and finally, there is the cost of the exam itself.
It isn't cheap - but nothing that is worth having comes without a price and some sacrifice. Being an IBCLC should not be viewed as a hobby, or something you can do "on the side" while your children are young. This is a profession, and the rewards are terrific!
That's a great question, and the answer varies depending on where you are working, and in which part of the country you settle. Hospital-based lactation consultants will probably make as much or slightly more than a staff nurse; clinic and physician-offices will pay slightly less. One study estimated that the median pay for an IBCLC working in a hospital full time is over $60,000/year. IBCLCs in private practice -- well, it depends on how hard you work at developing your practice, the particular needs of your community, and what the market will bear.