Working as an ESL teacher without being a native speaker?

You can but it's more difficult to find a job because they like native speakers. Also, you wouldn't get paid as much by a substantial amount. If you still want to pursue it, you need to be sure that your grammar is impeccable and that you have a clean accent. 

Pay will vary greatly depending on the position and the location. Rural and smaller cities will have lower salaries. Universities pay the lowest. International schools would probably offer the highest pay but it would probably be more difficult to find a position as a non-native speaker. The range I'd guess could be 8k-20k/mo. 

Something to keep in mind is if you are ethnically East Asian (meaning, you LOOK Asian) it will be far more difficult to find a job. They have no way of really knowing if you are not actually just Asian trying to pass yourself off as a foreigner (a realistic concern, especially in China since fraud and corruption are rampant there).

hello. he can take the TESOL certification and work in some Asian countries. But take note that many students prefer native speakers. However, the Asian teacher can connect with the Asian culture and native tongue explanation.

Salary depends on the private school's policies and the level of proficiency of the teacher. Native speakers still command a much higher salary and the teacher may look elsewhere to other jobs for other options.