Found 2 exchanges where Helium is traded for EUR. According to the data on 6 September the most optimal price to exchange HNT for EUR is €0.504 for 1 Helium. This rate is fixed at Bitvavo at the maximum trading volume of the pair HNT/EUR - 524 ths. EUR.
The maximum daily trading volume is observed in the HNT/USD trading pair at Coinbase Pro and reaches € 3 221 933.87 (0.157% of the exchange's total trading volumes) at the price € 0.522 per 1 HNT.
The minimum price to buy HNT for EUR is 0.504 - on the exchange Bitvavo.
The maximum price to buy HNT/EUR is 0.511 - on the exchange Bit2Me.
Warning: some HNT markets show an abnormally wide spread — those quotes may be unreliable (thin liquidity or off-market trades). Cross-check the volume against several venues.