How far away was DS9 from Bajor?

Maybe they just number the planets from outside to in, instead of sun-out like we do.

Are you sure this is correct? According to the official Star Trek: Deep Space Nine Technical Manual,

Still, you’re right that the distance from the station to Bajor probably varies, since the belt’s orbital plane is inclined to that of Bajor, and because the wormhole, the belt, and Bajor all have different orbital periods.