I mean you no disrespect, but you don't have a clue of what you are talking about. I hope you are not an accountant. I am a CPA, though. So, let me give you some numbers:
With $120k of debt coming out of law school (I'm rolling undergrad debt into this) and a loan amortized over 10 years at 9.5%, your minimum monthly payment would be $1,552.27. If you amortized it over 30 years through consolidation, you would pay $1,009.03, assuming the same interest rate. Let's go with ten years at 9.5% (which is a little high). Your annual aggregated loan payments would be roughly $18,600. So, lets assume that you make $60k out of law school, just for argument's sake. I estimate federal and state taxes (with no material deductions) to be roughly $9,600. After taxes and loan payments, you have $33,700 (roughly) of disposable income. That's more than I make now after taxes and student loan payments. I live just fine, drive a new car, and live in a nice neighborhood. I'm not wealthy, but I have no trouble living and saving money.
Now, I don't know if you can move from a boutique firm to big law. I don't see why that is not possible, but I have no facts one way or the other. I can only speak for the accounting profession. It's very easy to move from a small firm to a big 4 firm. Why is law different? Maybe it just is.
Now $60k may not be enough in CA, NY, DC, ect. It's more than enough in Las Vegas, Phoenix, New Mexico, Utah, ect. So, if you plan to practice in CA, you might be in trouble with large sums of debt and job prospects that fall short of the largest firms. Those are the breaks of trying to compete in saturated markets.
If you take the free school, you have much more wiggle room.