There is no current plans for an app, largely because our base platform - Xenforo - is well designed to be fully functional and to run smoothly on mobile devices. The built in alert systems can also be setup to an e-mail that can in turn be set to send phone notifications so you can receive alerts notices via your phone.
So it's less of a financial issue, and more of a 'not really necessary' issue.
I regularly get notices, read, and reply to posts via my phone. Even built an entire Epic Roleplay forum via my phone once without any issues. Not much that an app would really provide, that the site can't handle all on its own.