I've spent over $9k and lost at D3, not sure D2, I've spent close to $60k and lost at D1, and multiple times spent $45-$50k.
I don't have spending limits, it all depends on situation, but 3x or 4x what a scholarships "costs" is when I start to feel like it's getting pricey. And fighting, and losing, the prestige battle at D1 can burn through cash quickly.