Where is the resistance in a starter motor circuit?
You are correct. 

The coil in the relay has many turns of thin wire and, as such, has higher resistance and draws much less current than the motor which has a few turns of fat wire with low resistance.

The relay is used so the switch can be smaller and won't burn out due to arcing. ALso so you don't have to run 1/4 inch cables all the way up to the steering wheel.

The current consumed by the motor does however drop off as it runs up to speed. It's initial in-rush current is very large though. Since starter motors are only ever really engaged for a brief second or three, it's almost always operating in starting mode. (Pun intended)