Interactive Brokers has a very robust API, and market data fees are $10/month or free if you spend more than $30 on commissions.
(I'm not affiliated, but I've used their services before and have been happy)
(I'm not affiliated, but I've used their services before and have been happy)
IB's API is anything but robust. It is inconsistent, poorly documented, and IB have a history of changing it without notice.
It also requires all communication runs through their client side Java GUI app, which is also prone to a variety of problems.
That said, IB are a very good low cost broker with amazing product breadth. But I would suggest caution if using their data API for anything remotely serious.