If you are just starting with limited capital I would try Just2Trade, they offer stock trades at $2.5 a trade or $2 if you have an account size of 50k or more. You will need a charting platform though such as Quotetracker and use Just2Trade data to feed it, you can also execute trades via QT. I have been a customer of Just2Trade for a few months and their customer support via phone is very good for such a discount broker. They have the lowest margin rates in the industry and offer about 4.25% on the money market account.
Sorry, missed the intention of the poster, Just2Trade do have an API platform but never used it to automate trades.
Sorry, missed the intention of the poster, Just2Trade do have an API platform but never used it to automate trades.