Alpaca is a commission-free stock trading API. I wasn't able to find any node that connects to this service so I wrapped their official NodeJS SDK into a node-red package. Easy as pie!
Stay tuned, as this is definitely a WIP: https://github.com/mdkrieg/node-red-contrib-alpaca
The provided example flow is designed to submit a number of limit orders, evenly distributed over a given price range.