If you are trying to minimize your expenses from sending transaction, consider this bit from https://en.bitcoin.it/wiki/Transaction_fees
A transaction may be safely sent without fees if these conditions are met:
It is smaller than 1,000 bytes.
All outputs are 0.01 BTC or larger.
Its priority is large enough (see the Technical Info section below)
Otherwise, the reference implementation will round up the transaction size to the next thousand bytes and add a fee of 0.1 mBTC (0.0001 BTC) per thousand bytes. As an example, a fee of 0.1 mBTC (0.0001 BTC) would be added to a 746 byte transaction, and a fee of 0.2 mBTC (0.0002 BTC) would be added to a 1001 byte transaction. Users may increase the default 0.0001 BTC/kB fee setting, but cannot control transaction fees for each transaction.
Bitcoin-Qt does prompt the user to accept the fee before the transaction is sent (they may cancel the transaction if they are not willing to pay the fee).
Note that a typical transaction is 500 bytes, so the typical transaction fee for low-priority transactions is 0.1 mBTC (0.0001 BTC), regardless of the number of bitcoins sent.