Mobile app for planning apartment renovation budget by stages

I'm planning a full apartment renovation and want a mobile app to keep the budget under control from start to finish. The idea is simple: the renovation is split into stages — demolition, rough construction work, utilities, finishing — and each stage gets its own planned budget. As money actually goes out, I enter the real expenses under the matching stage, and the app should immediately show how far I've drifted from the plan, both for that stage and for the project as a whole.

What matters most is a clear picture of the gap between planned and actual spending, not just a list of transactions. I want to see which stage is running over before it eats the whole reserve, ideally with a simple progress indicator per stage and a running total across the project. Expenses should support a short note and a category (materials, labor, delivery), plus an optional receipt photo.

The app needs to work on Android and iOS, store data reliably (local storage plus backup; cloud sync is a plus but not required for version one), and stay usable without explanation — I'm not a construction professional, just someone managing my own renovation.

Please include in your proposal:
— experience with budgeting or expense-tracking apps
— your approach to structuring stages and categories
— rough timeline and cost for a working first version