How much would the total cost be to adopt a child from cameroon using an attorney from cameroon and not the united states?

There is no way to figure such a thing since it depends upon the individual attorney fees, court fees, how often they require that you come to their country to be interviewed/investigated (and whether there is a charge for that), whether or not the woman who has custody is seeking financial recompense, what the going rates for hotels/airfare are at the time of travel, as well as how long you need to stay. Also, some countries require that you pay an exit fee of sorts to take the child out of their country, ans you will be responsible for providing a visa for that child. I know this doesn't help much, but to give you an idea, you are looking at $10,000 or more most likely. Also, I would seek the advice of an attorney here in the states to protect yourself.
Cameroon has specific laws on who can adopt a child, here are some:

Either one parent in the couple is over 40,
OR
One has to be at least 35 AND have been married for 10 years.
The prospective adoptive parents must be at least 15 years older than the child to be adopted; however, if the adoptive parent is married to the biological parent of the child, the age difference must only be 10 years.
Couples who do not meet these requirements can submit a medical certificate confirming the couple’s infertility in order to have the age requirement waived. They may bring a medical certificate from a U.S. or local doctor to do this.
Both parties in a couple must be in agreement over the adoption. One spouse cannot adopt without the other’s permission.
Both spouses must be medically fit to care for a child, proven by a medical certificate from either a U.S. or local doctor.
Evidence of financial capacity; this is usually proven with a report of a home-study from the U.S. along with bank statements, evidence of assets, pay slips etc.
Evidence of the consent of the birth parent(s) (if they are alive). The consent must be witnessed either in court, by a diplomatic mission or by a public notary.
Evidence of the consent of the adoptee if the adoptee is 16 or older. The consent must be witnessed either in court, by a foreign consular officer or by a notary public.

Two forms of adoption exist in Cameroon, the so-called " simple adoption " and the " adoptive legitimization " The decision of a simple adoption a
magistrate or notary adopts and later it is approved by a civil court. The decision of an adoptive legitimization is of judicial character. There corresponds the competence in the Top Civil Court of the domicile of adopting.

Simple Adoption - supports ties of affiliation between the child and his biological family. It creates a tie of affiliation between the child and the adoptive family. It is revocable for serious motives.
Full Adoption - The form of adoption so-called " adoptive legitimization " is only possible for the children younger than 5 years, orphan, godforsaken or of unknown affiliation. It has the following effects: rupture of ties with the natural family. It creates ties of affiliation between the child and his adoptive family. The decision is irrevocable.

Sorry I couldn't be more helpful, Good luck Susu