Is there an option for using Design Systems without being an "Enterprise"?

Yes! There's a Professional Plan117 which I'm on right now. But honestly, their DS is still a baby compared to popular tools like ZeroHeight or InVision DS! Design System Libraries of UXPin is great but at the same time, DS as a product/flow still lacks tones of features! But if you have a client's demand or want to give it a shot, go with it!