its not as simple as that. the tax free break only works if you stay out of the country for most of the year, you can't be in nigeria then come back every month like that, there is only a certain amount of days you can come back home and still keep the tax exempt status.
i know this because my brother works in iraq, and he is allowed to come back into the country, but he can't come back whenever he wants, if he stays for too many days has has to pay taxes. it sucks.
and if your making 30k a month and paying taxes on that would be hell. and its never as good as it seems. you going there and making that much money is HAZARD pay, because you can get killed etc