Azure Websites also offer Node.js hosting [1], and they have a free plan for small (development) sites. Paid plans there seem more expensive.
And in most cases providers do as much as possible to lock you in, so you don't switch to a cheaper option when you reach certain size.
On the other hand, we want customers to know that they can leave us whenever they need to. Your apps are completely portable, so there is no reason not to give it a try.