Where can I find inexpensive eyeglasses in NYC or Brooklyn?

This doesn't answer your question directly, but you should consider buying glasses online. The prices you can find are much, much cheaper than in stores. I haven't bought glasses online yet, but if you want to save some money you can start by reading this blog post, titled "Eyeglasses stores are for suckers": http://glassyeyes.blogspot.com/2006/11/from-3mew-eyeglasses-stores-are-for.html

I'm not sure if it's as fast as you'll need, but you could spend 50 or 100 bucks instead of 200-300.