Staffords and private or Grad PLUS loans are your guaranteed fallback.
My program has a small amount of scholarship money available, worth up to $4,000. The rest has to be covered through loans or private means. The Department of Education is forcing postbac certificate programs like Goucher and Bryn Mawr to be reclassified as graduate certificate programs. This creates a lot of hassle for the programs, but it does open up more funds both in terms of Staffords (graduate rather than undergraduate loan limits) and Grad PLUS loans also become available at that level.
If you're going the self-directed route, private loans like Citiassist loans can make up the difference between Staffords and actual cost. If you're not in a full-time program, you can obviously also work part-time. If you're in a full-time program and would rather work part-time to avoid debt, you'll have to get over yourself and just accept that the debt is worth it if it gives you more time to study and attain higher grades.
The cost of doing a post-bac is, I'm afraid, quite intentional. You have to be committed to switching to medicine. If you get into med school, the cost will pay for itself many times over, and the accumulated debt will roll into your med school debt. And if you don't get into med school...well, there's a Darwinist component to it all. Life's all about calculated risk. Unless you have an adverse credit history, there's always enough money out there, and then it's a matter of whether you think becoming a doctor is worth the financial risk versus the uncertainty of admission.