I believe blockchain.info charges 0.01 BTC/transaction, regardless of number of inputs/input age.
Their
FAQ says:
Are there any fees for using My Wallet?
No it a free service. You maybe asked to include a "miners fee" to help support the bitcoin network (See question below).
Why am I being asked to include a "Miners fee"?
A miners fee will encourage bitcoin miners to accept your transaction more quickly. Sometimes if you don't include a fee your transaction will never get confirmed and will be returned to you in approximately 24 hours.
The "will be returned to you" bit is news to me. How is that even possible? Some miner may include the transaction after 24 hours.