How many bitcoins would it require for a sustained DOS attack on bitcoin network? How many bitcoins would it require for a sustained DOS attack on bitcoin network?

Without transaction fee, how many bitcoins would that be?

How many transactions could we generate with 1 BTC everyday (without fee)?
7 transactions per second times 60 equals per minute times 60 equals per hour times 24 equals per day = 604800 satoshis sent in individual transactions.

However, nodes filter such so-called "dust" transactions. The minimum output amount for a transaction to be relayed by the network is 546 satoshis. So: 330220800 satoshis = 3.302208 BTC to fill the network for a day. 

(As explained in, http://www.reddit.com/r/Bitcoin/comments/37z9ln/how_much_btc_needed_to_fill_entire_1_mb_block/crqzv63)