How high are transaction fees for "sendmany"?
Is it correct that using "sendmany" i can send Bitcoins to multiple addresses but only have to pay the transaction fee once?
The transaction fee is based on the size of the transaction (in bytes), among other factors. Each output adds some length to the transaction, so more destinations will mean a higher fee. With the current transaction fee schedule, roughly every five destinations adds an additional .0005 BTC to the standard fee.