Musette,
We adopted quite a few years ago and used an agency in San Antonio called Adoption Services Associates. There have been some changes since that time but the agency still operates for both domestic and international adoption.
Our adoptions were not inexpensive once you add in agency fees, last trimester support for the birthmother (not sure on the status of this now), travel etc. That said, there are tax breaks now I believe. In addition, for our first adoption we gook out a home equity loan to pay the costs up front and paid it off over two years. There are usually ways to come up with the money and with domestic adoption you have a somewhat better sense of what things will cost than with international adoption. In addition, you don't have the large travel costs.
Finally, the cost of the adoptions pales in comparison to the joy of raising our children. On a lighter note, now that our children are teens the costs of adoption seem low compared to auto insurance, college etc.!
Good luck and feel free to contact me privately if you need more information.
B.