There is no "cheapest marble" — no such ranking exists on MarbleMap, and we deliberately never name a stone for you. Recommending material would mean taking a side in your project, and a neutral market cannot do that.
The question also has no stable answer. Cheapness is a property of a job, not of a stone: a variety that is economical at 300 m² in one finish can be the expensive option at 40 m² in another, or once its blocks have to travel further. Anyone who hands you a single name is guessing at your quantities, tolerances and delivery point.
What you can do instead is invert the question. Rather than choosing a stone and then hunting for a price, describe the outcome you need — the look, the finish, the surface area, where it has to arrive — and open a New Demand on the Category that covers it. Suppliers who actually quarry and process that material bid against your brief, and each is free to propose the variety that comes out cheapest for exactly your job. Suppliers can also ask you questions inside the demand, so an unfinished spec is not a blocker.
You then compare the answers rather than the theories, and the choice of stone remains yours.
Also asked as: Which marble is cheaper? · What is the most economical stone? · Can you recommend a stone for me? · Which marble should I choose?