Insulation under the floor slab EPS or XPS?

If I simply scale linearly, my prices for 40 cm GSS come to about €65/m² and 0.28 W/m²K or alternatively with 14 cm XPS to €46/m² and 0.25 W/m²K. In that range, you can notice the price difference quite clearly; at 35-40 mm, GSS would have been cheaper.

I made a chart with total costs vs U-value



Edit: Changed the chart to unit price per m².