That's the thing: You aren't managing a budget. Not really. You're paying hirelings on a set schedule to prevent banditry (which they don't seem to do very well) and to defend your stronghold (currently bugged, with hirelings becoming hostile after battles; also unnecessary since the player can return to defend the stronghold themselves), while tax income is produced essentially randomly. Budgeting would involve managing a mostly predictable stream of income efficiently and accounting for both predictable and random expenses.

I've found the single most effective strategy to be simply dismissing all hirelings and reloading a quicksave when a particularly big loss occurs after completing a quest. Because of that huge random element mentioned earlier, a simple redo often produces dramatically different results.

Trust me, I don't mind good budget management systems. I've played, enjoyed, and beaten games like Alpha Centauri, Galactic Civilizations II, etc. I'm hoping that we'll get a patch that significantly improves the stronghold after essential bugfixes are completed (broken/awful talents are a much higher priority imo).