I think, in principle, he should be paid at a rate consistent with the size of the church, his experience, and his level of responsibility.
All other things being equal, why should the pastor of a church of , say, 500, be paid differently in a poor area than a wealthy one? He's doing the same work. "The labourer deserves his wages" (1 Tim. 5:18).
Conversely, if a poor church can't afford to pay a full-time pastor a decent enough wage to support his family and build up some equity, then they need to accept that he has a right, perhaps even an obligation, to be bivicational.