In some cases, American citizens who live abroad might qualify for scaled tuition. If the majority of your income (50%+) comes from the economy of your country of residence, then yes! Your tuition will not be as discounted as someone whose sole income comes from that country but it will be scaled according to the source of your income.
If the majority of your income (50%+) still comes from the USA, then unfortunately this is not available to you. Many missionaries in the past have had success fundraising specifically for their continued education. Speak with your donors or sending agency about this.
Please note, you may be asked to provide proof of the source the source country of your income.