I would start off with which country I wanted to hunt in.

Buffalo:

Zimbabwe
Zambia
Mozambique
Tanzania
South Africa (but its expensive for buffalo)

You can pick from a sort buffalo hunt - 5 to 7 days, or a longer hunt - 10 to 14 days. The longer hunts are recommended if you want to hunt for a bigger trophy. Generally on shorter ones you may take the first representative head found.

Zimbabwe will have the lowest prices but you take the countries political climate as it comes. Tanzania would be a great hunt but a little more expensive.