All over Germany. As a student, I donated blood plasma which was way more lucrative (until the US banned plasma imports and killed the market). You can donate plasma more often (up to 5 times in 14 days), and IIRC I got 17€ per session, 30€ for every 3rd session, and 50€ for every 5th session. Yes, they had a consitency-reward schema going on in order to get you engaged and keep coming back. Plus, also wanted to thwart off people in financial needs that desperately need money the next day (like drug addicts).