That's why I think it might be a better idea to get accepted to a state school after doing an SMP rather than a private school. If you look through the MSAR, you'll see that the average state school tuition hovers around $20,000-$30,000 per year (not including living expenses) but most private schools charge $40,000-$60,000 per year. If you multiply that over 4 years, going to a state school might save you $80,000 in the long run. This is especially good if your SMP can help you establish state residency.
That being said, I finance the SMP degree the same way I finance any other degree - through loans and savings. In the long run, $40,000 isn't that much if you consider the fact that most people graduate medical school with $200,000 in debt. It's the same for law, a lot of people are willing to put themselves in >$40,000 of debt, even in a bad economy when layoffs are eminent at almost every large law firm. Unfortunately, it's the cost of doing business, especially if your undergrad GPA was not that strong.
There are quite a few reputable SMPs out there that are about $20,000 if you look around hard enough. I think you can find out more about those programs in the stickie at the top.