Honestly, before you drop a grand, you gotta think about how you handle your gear in the wild. Reliability is basically the most important thing for me because street photography often means being out in less than ideal conditions where stuff can get bumped or caught in the rain. I have a couple of questions to help narrow it down:

• Do you often shoot in dusty or rainy environments where weather sealing is a hard requirement for your peace of mind?
• Are you looking for a metal build that can survive some heavy daily use, or is low weight more important for your style? Personally, I always prioritize a lens that has a reputation for bulletproof autofocus and solid construction. There is nothing worse than being in the middle of a perfect candid moment and having the autofocus hunt or the barrel feel flimsy in your hand. I would rather have a slightly heavier lens that I know is gonna work every single time I press the shutter. Reliability is key when you are doing candid work because you usually only get one shot at the scene before it is gone forever. As for focal length, are you the type who likes to blend into the background from a distance, or do you prefer being right in the middle of the action?

I've used the Sony 35mm f/1.8 for years. Sharp, fast focus, and easily found used under $400.

Forget just focal length! Consider the Sony FE 40mm f/2.5 G. Compact (45mm length!), great for stealthy street. Its linear motor gives amazing, silent AF - crucial for candid shots! Plus, the minimum focus distance (0.28m) lets you get surprisingly close when needed. It's sharp wide open too! You might find it used around $500, leaving room for another prime later!