Base price of an M3 usually falls right within a few hundred of a fully loaded top end 3-series coupe.
The E46 M3 started with a base price of $46,995 back in 2001. A fully loaded 330Ci came in around $47,500-48,000.
Expect to see the same pricing strategy with the new M3. A fully loaded 335i coupe runs around $55k. The new M3 should start right around that price; perhaps $54,995 or $55,995.