Less than buying a new car. Many, many people are simple, middle class like you and me. Some are single women and men who are teachers, accountants, business owners. ALL of the money is NOT due at one time. I know of many families who save as much as possible for one year, then begin the process, knowing it will take another year to get together all the paperwork and complete the adoption.
Some countries have more children available of one sex than another.
Sometimes when you already have a child of one sex, you will be allowed to request a child of the opposite sex. Knowing this now can help you to choose a country to work with, and give you questions to ask of an agency you are thinking of working with. It depends on which country you choose to work with, which agency you choose, how fast you personally gather your documents together. How dedicated you are to getting this adoption done in a timely matter. Yes, many things will be beyond your control.