You're creating a new product to simplify peoples' life. So first of all you need to learn who your typical user is. Their average skill level, typical workflow and so on. Your decisions should revolve around your target users.
Having a small budget is actually a good thing. That way you will have to do most of the user experience work. Steve Krug's books are a good start.
Do not let topics like information architecture, personas, wire-framing etc. get in the way. Use whatever feels most natural. Research your intended users, research your competitors and common complaints on their forums. Use pen and paper to sketch block diagrams of your user interface, and create numbered sequences of them to represent workflows. Use rough sketching. The point is to visualise and discuss ideas.
Once you have all these in place start coding and fleshing out the real product. Then start using it internally. When you feel quite confident target a beta of the product to get real feedback from users. User feedback is invaluable.
Finally, as you are approaching the end of your beta period, I would suggest using your budget on a service like usertesting.com to get people fitting your target to try out the product and get more valuable feedback.