What would be leaking at the back axle area - by right rear tire?

What year, make, model? Depending on the vehicle, it could be an axle seal. It could also be brake fluid.

What year, make, model? Depending on the vehicle, it could be an axle seal. It could also be brake fluid.

Honda - CRV - 2003
Is axle seal expensive?

The seal itself is not too expensive. The whole job will likely cost several hundred dollars.

All wheel drive or 2 wheel drive? 2 wheel is pretty basic, just a greased bearing. All wheel is much more complex as to leaking oil, if that's what it is.