Interactive brokers offers low fee access to their platform (https://www.interactivebrokers.com/en/index.php?f=13869)
Quantopian (www.quantopian.com) gives you the ability to trade through robinhood with long trades at 0 commission. There has been some skepticism in the Q forums on how well robinhood's execution is (possibly the effect of a "you get what you pay for"-attitude).
Trading real capital with algorithms is more difficult than it sounds. Mentally if you're algorithm is doing stock selection as well as trade execution, you no longer understand what you own. During a period of extended drawdown, you have to be mentally tough enough to believe that your algorithm has what it takes to dig itself out.
In a sense, it is like the start-up game. You have to believe you're doing something well enough that in the end you'll be right (and not bankrupt).