How should I budget a curbless shower with a concealed linear drain?

I’m trying to set a realistic allowance for a curbless, roll-in shower and separate the accessibility-related construction costs from tile and fixture choices. I’m deciding between a concealed linear drain and a standard center drain.

For contractor quotes, where does the main premium usually show up?

- Recessing the floor or adjusting framing to create the required slope
- The linear drain and concealed grate assembly
- Waterproofing and tying the shower membrane into the bathroom floor
- Extra tile layout and finish work at the entry

I know the answer will differ a lot between new construction and a remodel, especially on a slab versus a framed floor. I’m also considering larger-format tile, blocking for future grab bars, and possibly a fold-down seat later.

For those who have priced this out, what would you expect the curbless-shower construction allowance to be compared with a standard shower, excluding the toilet, vanity, faucets, and other fixtures? Which line items would you insist on seeing broken out so a low quote doesn’t skip recessed framing, waterproofing, or finish transitions?