Oh right, well you need to be sure you can lay wooden flooring on it. Wood is a natural insulator so it could actually inhibit your underfloor heating, hence the reason it is more suited with tiles. You would have to turn it up significantly, and as engineered timber is really the only suitable wooden floor you could use the manmade core can inhibit it more.
Also you can't run it tight against the marble, as your floor will need to expand and contract naturally due to the changes in temperature, which again will be increased due to the underfloor heating. So you will need a 12mm expansion joint around the whole floor.
I will come back to you on prices but for the thickness of floor you are looking for, its pretty much in line with the market average.