600$ is stretching it for your shopping list I think.
Even if you find a 300$ gun good safe eyepro is around 100$ after it's in your hands.
kneepads are a good idea.. elbowpads are not needed.
2-3 extra magazines if you're using high caps are around 50-60 bucks
You might be able to sneak in around 600... don't be surprised if you're around 800 all said and done.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.