You'd bet wrong, especially on the east coast where I'm alone working on science fiction productions. SAG people are the only ones with the right experience for science fiction, especially my friend who has made a career out of it. With the SAG/AFTRA merger more and more of my cast is turning SAG. So, it pays to continue to work with them. Plus, we can get names attached like The Vampire Effect did with Jackie Chan, if we need to go that way.
SAG, British Equity, and Eastern European Union actors are much higher caliber than non union actors names or not. They take their acting more serious and snap at the non union people who hold the production back from their laziness.
We had an actress born and raised in the USA non union who made up her own hours and when the shooting days came, she kept getting lost finding the shooting locations. Our Eastern European Union actress found every location and was always on time. She snapped off at the non union actors with all the excuses who could not find the shooting locations and trying to reinvent the shooting schedule. I ended up firing the American born actress for bad attendance. We had another American born actress who gained 40 pounds from the time we got her costume measurements. She could not fit into her costume and was too sick and over weight to do stunts. As my friend from the Hollywood studios advised me, go union and watch these problems vanish.