I would love to tell you that you can easily find 500sqft. of space for $1800, but the fact of the matter is that it would be somewhat of a challenge. However, if you are patient and stick with the right broker you can certainly find something for that price, but realistically, it would be a bit closer to the 400sqft. mark.
I recommend looking into average sq ft pricing in different NYC neighborhoods on blocksy.com.
I hope this was helpful. If you have any further questions feel free to contact me.