I researched US brokers earlier this year, I think you have already found the cheapest in Deep Discount Trading for the size you quote. Your a/c will actually be with Crossland LLC. For account opening you won't find anyone better than Howard at DDT, although had a few issues with Crossland themselves, like debiting a credit!!
I have sinced moved to Dorman, mentioned earlier in the thread, they do CTS T4, decent CS and intraday margin rates, contact John Texidor there for an individual quote, probably 20 c more per r/t which was worth it to me for consistent margin rates across a range of products. Also mentioned earlier was Advantage, I hear good things but you'll only get half of exchange margin for day trading unless things have changed, which may affect your strategy, and a strict min $10k to open an account here.
Good luck.
I have sinced moved to Dorman, mentioned earlier in the thread, they do CTS T4, decent CS and intraday margin rates, contact John Texidor there for an individual quote, probably 20 c more per r/t which was worth it to me for consistent margin rates across a range of products. Also mentioned earlier was Advantage, I hear good things but you'll only get half of exchange margin for day trading unless things have changed, which may affect your strategy, and a strict min $10k to open an account here.
Good luck.