Go to this website
NACAC | Adoption Subsidy
to find all kinds of good stuff about the adoption subsidies offered in each state. There are definitely some that are much better than others. For example, in NC, they basically give the monthly foster care payment to the adoptive family with no negotiation necessary. I am currently adopting through NV, and they don't want to give me a dime. I am fighting for everything, including Medicaid coverage.
Hope this site provides the info you are looking for. And to answer your other question, it is my experience that the subsidy is only negotiated AFTER the child is placed with you (during the 6 month period prior to the adoption being finalized).