Howdy!
Personally, I'd look into something else in the open-source community like Ruby or Python.
Both are free, have great frameworks (Rails, Sinatra, Django) for API/web, strong community support and great PAAS options like Heroku. Also tons of free, opensource modules for both - everything from authorization to image manipulation. Building a RESTful API in either is very straight forward, and well implemented code in either can be incredibly fast (many services you know use one or both).
I'd also recommend sitting either on top of Postgres DB (assuming you're going to need some kind of data/state store). Figuring you're on a Mac since you're talking about iOS development, so you've got both of those languages OOTB (though you'll want newer versions, frameworks, etc.), a good editor, a DB ... good news, it's all free 🙂