The €30k to €35k per year they make in this context approximates to free. Any normal company has to pay much more than that for less. A non-phd software engineer will get paid much more to change button colors for example. So that can't be the reason they are expensive and a PhD candidate is doing many other things than just helping to run trials.

> Any normal company has to pay much more than that for less

In most EU countries, the employee receives much less than what they cost the employer. In France, if an employee gets 30K euros, the employer has to provision ~45K Euros.

Also as much as it pains to say, 30-35k Euro is high salary there. :(