No return flights under €100 for 3-5 day stays right now. Try a direct search on Aviasales with your own dates.
Period
Next 6 months
Stay length
3–5 days
Maximum
€100 per person (return)
Prices refresh hourly. "Direct" takes you to the airline's own site with details pre-filled; "All offers" shows alternative sellers (Kiwi, Kupi, and others) via Aviasales.