Termostat replaces 850

Hi again, my little one is just doing a little trouble again. 850er/2,5L/144PS/10V And it doesn’t get warm any more. As long as you drive, the needle doesn’t get a mm from the basement. After 15-20 minutes. The needle is located where it belongs. In the middle of the display. Then and only then it gets warm in the car. Now I thought, change the thermostat. Can’t be so expensive. My friend told me that he should lie around 90-100€. I passed out slightly. Is it really so expensive? Or is it such a thing here? look if this is the right thing, I’ll probably open a spare part booth soon. Can I take it? Or am I completely on the wooden path?