Any direct access broker will provide quotes through their execution platform. Check lightspeed or talk to some prop firms. Even the lower tier ones since all you want is the quotes. Realtime data will cost you no matter how you look at it. Most retail brokers (like TD, Etrade) do not provide quotes to all ECNs.
I guess, if the "you" in question is a dirtbag. If that's the kind of business transaction that appeals to "you", "you" can also sign up for a book-of-the-month club with a fake name, grab all the free books... & etc.
wtf you are talking about? business transaction...book-of-the-month..you should quit smoking, you know.. who are? my mom?
Essentially, an XML based API is platform agnostic and can even be accessed through a common web browser. Most of the other quote API use sockets and cannot be easily utilized from a web scripting language (i.e., PHP, ASP, Python, etc) but must be processed via a more sophisticated language such as Java, C#, etc.