I do understand that most art shows work this way. I also know that most art shows I've been to don't display 20,000 postcards, nor are most patrons willing to

I do understand that most art shows work this way. I also know that most art shows I've been to don't display 20,000 postcards, nor are most patrons willing to spend $33 to buy a postcard. However: using your "art world" connections might not be a bad idea. Why not speak to some (financially) successful artists/gallery owners that you know and ask them how they'd raise money in your situation?