Ask your builder.

Not possible right now. But thank you

Easily double, possibly more floor system dependent, as the system needs to be dropped/recessed. Is this a production type home, custom, semi-custom? I ask because a production builder may not be able to pull it off and the flooring systems are just at code and may not be able to be modified for a curbless install.

A correctly done shower is 10-20 with glass. Double that for curbless. Easily. Depends on size and specs.

A curbless shower is a bit more work, but I find double difficult to believe. They aren't all that.

@Mint tile Minneapolis linear drain is the best option? so basically the floor slopes in one direction toward the shower head vs different angles sloping toward the middle?

You can also have a linear drain run the full width (or length) across the center, and have the shower floor slope in from each end. That way you only need half the amount of slope in the floor. That's what I did when we remodeled and wanted to leave the drain in the center.