Has there ever been a challenge to get the best roast out of cheaper beans? Probably anathema to the ferrari gear crowd and the gesha enthusiasts, but a fun puzzle for me. Like making for dinner whatever's in the cupboards.

Roasting Ethiopian Djimmah grade 5. 10lb sacks get down to $4.80CDN/lb at green beanry (which i can pick up in person now my other half lives in TO)

There is work sorting the bad beans but the roasts taste good to me.

I guess most (or all) professionals face that challenge every day.
For me, as I'm roasting coffee for myself and maybe a few friends now and then, the challenge is finding good coffee at the small weights that I buy (similar to most of us here). When buying say 10 pounds and having 3 varieties to choose from, that choice is easy. The reason for this is simply that I don't need to consider the economic part as much as I want to get the best cup that I can find and roast.
Making a living out of it is a different story. There's the business part in it which makes for most of the equation. Finding and balancing greens with good enough taste at a good enough price. From my amateur perspective, I guess (again) that what makes a successful professional roaster is the way he or she runs the business, not being the better roaster by .2 in the cupping score.

I've had some pretty darn good espresso made with low grade beans, including robusta. The trick seems be in in knowing how to blend.