Basically, any exchange with SEPA deposit option should work. For most exchanges the fees will decrease with increasing volume, just check some exchanges like
Kraken or
Bitstamp. As shorena wrote, keep the KYC and AML stuff in mind, you might check with your bank prior 'high volume' deposits. Not sure at the moment, but 10 or 15k € should be the critical mass.
As an example, if you want to buy
BTC for 5k € at Kraken this will cost 0.19% fees and need a basic verification, should not cause any trouble.