[R-SIG-Finance] API based Trading Lowest Commission

[zubin]

Hello List,

Looking for recommendations for the lowest cost brokerage, that has an
API we can utilize for automated trading.  

Trading US listed ETFs. 

IBrokers, for about 700 shares a trade, 50$ a share, is about $8.00.  
Each trade will be in the $35K range, 500-700 shares. 

Does anyone recommend alternative brokers (with an API) that are less
expensive, i was erroneously assuming $2 to $3 per trade?