Vicki,
PA laws are: the birthmother may sign 72 hours after the birth. Consent becomes irrevocable 30 days after the birth, or 30 days after signing, whichever is later.
I agree with tobeafamily, your costs should not be more than 10K.
It was my understanding that potential birthmothers are not bound to a particular agency. You said "signed" with an agency, does that mean that an agency made the birthmother sign a contract? I'm not sure this is allowed. I would check with an adoption attorney.
If you are in the Philly area, I know a great adoption attorney, feel free to PM me. If not, you can search for one at
http://www.adoptionattorneys.org/
Good Luck!