Looking for reversible thermo chromic pigment or paint

Hi, I am looking for reversible thermo chromatic pigments (or paint / ink, even paper) in europe. For now, the best I've found is 480€ including shipping and VAT for 1kg of pigment (32°C), which should allow to make about 5kg of paint, which would allow painting 20-25m² (one layer). If you add the price for white paint, is come to 25€ for 1 square meter, which is not so expensive, but I need half a square meter, not 20 ! Any advice ? Thx, tReg.