Check out Gladney and Buckner. I think it's Gladney that is in Fort Worth and has adoption seminars for domestic and international that gives a good overview of the process. You can register for the seminar at their websites. I didn't use them for my agency, but it was a good overview. Also, research books on-line regarding the process and read multiple books/workbooks to get a good understanding of the process. There's a fabulous adoption attorney in Fort Worth, and I an PM her info to you if you'd like. She has a good overview of the process for potential clients, as well. I also recommend reading "The Pumpkin Patch" to get a good feel for the international adoption process (you'll have to order it on-line...Amazon has it. It's a bit dated now, but it's a good general diary of the process). Also, read the first few chapters of Attaching in Adoption to understand the particular needs and differences of adopted children. For international adoption from eastern europe, check out the site frua.org. You can also look at adoption.com, although I sometimes have a difficult time navigating their site. Adoptshoppe.com also has a variety of resources. Also, check out the website for "Adoption Learning Partners," which is also a good resource for some of the required courses that you'll have to take as part of the process. If you are adopting overseas, check the U.S. Department of State for info on adopting from particular countries. My only caution is that the amount they claim it will cost and the reality of what it will actually cost are vastly different. It can easily be double what the U.S. government claims.
The best way to start is by researching agencies (do not feel that you have to use one that is local) and talking to an attorney. Once you have signed a contract with an agency and started the process, one of the earliest steps will be to complete a homestudy.
The Dave Thomas Foundation has good info on adoption, particularly adoption of foster children. It also has a database of adoption benefits from employers. You will want to check with your employers to see if either of your employers will reimburse any portion of the expenses and also to see their policy regarding time-off post-adoption. For example, my employer reimbursed a few thousand of the expense, but there was NO paid time off post-adoption. I had to use FMLA (unpaid leave) for time off. There is currently a tax credit that you can claim post-adoption that will help a bit. There are some programs that allow you to borrow against that as you go through the process. Also, if you adopt overseas, you will have to travel there at leasts once and possibly up to three times, and generally you will be expected to travel without your other children. So, it will almost certainly mean time away from them.
If you go through foster programs to adopt in the U.S., there are minimal (or even) no expenses. If you do a private adoption domestic or international, it is very expensive. The good thing is that the money isn't needed all at once, but there will be times when thousands of dollars will be flowing out at a very rapid pace. Bigger than the financial issue is that it is a very invasive and uncertain process. The rules will change on you frequently and seemingly without reason, and you will be asked (and requried to answer) a lot of questions that would normally be extremely rude. It is so worth it in the end, but it is a very frustrating process to go through at the time.