It's not clear from your question why you are considering a surrogate mother. In general, couples choose to have a surrogate mother carry their baby for them if, for some reason, the mother cannot carry a baby.
It seems that surrogacy is a more expensive option than adoption. Surrogacy requires fees paid to the surrogate mother (in addition to medical fees), to the agency who finds the surrogate mother for you, to the lawyer who draws up the surrogacy agreement, etc.
In addition, if you are opting for gestational surrogacy, in which you provide the eggs used, you would need to go through the egg retrieval process of IVF - this requires expensive medication, multiple visits to a medical facility, and a procedure performed in an operating room (the egg retrieval itself). This process generally costs many thousands of dollars.
You might want to get information about adoption in your area - sometimes adopting older children (over 2) does not require paying high fees.
Good luck!
Rachel