domestic infant adoption

Proud adoptive mom 6.11.09

So I know I have posted a few times as I have a son who is almost 19 who we adopted nearly 4 years ago. We have been going through fertility with no such luck and have been going back and forth about foster vs. straight adoption. I do not think I could do foster because I get attached easily and it would be hard when they left.  If we just adopt through local agencies  in our home town most of those kids are older. So right now we are looking into doing domestic infant adoption. We would be open to twins if the case ever arose. My question is when you do domestic infant adoption do all your cost have to pay up front. Also where is the best place to start with looking in to such?