it ought to be possible to avoid the ambition (…)
I disagree. At the beginning you always have a couple different ambitions to choose from, if you’re left with only the “battle standard” one it means you’re far enough into the game that 2.5k really shouldn’t be a problem. Unless you’re playing on the top difficulty, but then it’s meant to be punishingly hard.
You should never be left with only one (or two) ambition(s) to choose from. If the crowns for a standard shouldn’t be a problem, or if the game’s meant to be punishingly hard, that just means that there’s no reason why some of the subsequent ambition options (i.e. defeat a party of more than 12, or another mercenary company, or “blow it – we don’t need any restrictive ambitions”, etc. etc.) can’t be present. I fail to see how having a standard suddenly takes you beyond a threshold that makes you fit to select some of the ambitions that are only presented afterwards. I also fail to see why there can’t be an ambition to gather crowns to spend on better weapons/equipment (which, like the standard, miraculously appear out of nowhere once you reach the threshold).