We paid freelancers from around the world (via www.upwork.com) to write the questions based on some guidelines we made (it's not really hard to write questions

We paid freelancers from around the world (via www.upwork.com) to write the questions based on some guidelines we made (it's not really hard to write questions of this level so anyone can do it with a bit of guidance) and then paid medical students to write the solutions. Probably spent about $7k on this stuff back when it started, so it did require a bit of upfront cost.