Nikkor 16mm fisheye still about $350 to $500 depend on model and condition, in second hand market of course.
In store, you know could be more expensive.
In Spain, I bought my Russian Zenitar 16mm 2.8 about $150 not expensive at all, that I decided to buy it.
Quality is not too low, so it's great.
Ron, maybe in US, the Sigma one is enough cheap for you and you can conclude your dream. I am sure you didn't check if you can find a cheap one for very long time.
By the way, I will try to take my city ride tour soon and post any photo with it.
- Ron likes this