Hi, I'm not talking about commission. I'm developing an algorithm, according to which I buy/sell 200 shares of "C" at 11 am each day, but when I test my algorithm with history data, I don't know if I can take the historical market price at 11 am of each day as my transaction price, or should I add any transaction cost something like 1 cent per share because there is spread between bid and ask?
Get historical quote data - bid/ask is available through IB. Decide whether you'll be paying the spread.