Congrats on making the next step on your path to parenthood! We were well on the way to adoption before changing to trying IVF, so I learned a lot.
In general, if you are willing to adopt from your local child services dept, the costs are MUCH lower than private adoption. Many people shy away from this because they fear entanglements with birth parents, lack of info about prenatal care, etc...but its worth pursuing because you really never know and these kids really need a shot at being adopted. In MA children adopted from DCYF are given full scholarships to a state college or university. Many states offer other kinds of assistance, short and long term.
If you opt for a private adoption, definitely research agencies and meet with several. Find a social worker within the agency that you really trust (we got a social worker who did not work for us, totally scared us off, hence the switch to IVF - we were subsequently reassured that this woman was totally incorrect in what she told us, but by then we were too scared to continue). There are ways that you can lower costs, like only pursuing local adoptions, but if you are hoping for a quick process, the wider you make your search the better.
The biggest thing you need to decide now is do you want to do an open or closed adoption? If open, how open?
The Wendy's restaurant chain has a grant program for adoptions (the founder Dave was adopted) so check out their website. Also, the federal government gives tax credits for adoption up to $10,000 I believe. These are not exemptions, but actual credits, so money off of your tax bill.
Finally, if you are willing to consider international adoption, there are often programs supporting areas of highest need that will cost much less than other areas. When we were looking to adopt, it was Ethiopia that was in great need and the costs to adopt from there were significantly lower than from any other location, including the US. For Ethiopia, and several other countries, children can be escorted here so there isn't a need to travel if you don't want to. Though you might not get a newborn, many of these countries of high need process adoptions quickly so that they children are 3-4 months old rather than 10+ as with many of the more "popular" adoption locations.
