Compare quotes not opinions.

Seems a little low. Modern details are way more expensive than traditional.

Everyone complains about how much stairs and railings cost. I got so sick of hearing it, I stopped proposing those jobs.

It's a pretty good guess - could be more depending on the steel fabrication costs. My builder just put in some stainless cables and paid $8K just for the hardware. Working with steel his more expensive and required to get the open feel you are looking for. Labor is high due to the demand in commercial building for welders, etc. Expect it to continue to rise.

I used Atlantis Rail http://www.atlantisrail.com/ for a 29' balcony rail (a 22' straight section and then a 7' straight section. Posts and top rail was Ipe so those costs are NI) and it cost around $2K just in cable materials. I installed it myself which was very easy and if you do DIY the cable cutters only last for about 15-20 cuts so I needed 3 of those!

Very location dependant. And with zero sizing, pics or detailing info it is about impossible to even apply the wag method (wild ass guess).

Open risers...

"Modern" designs and detailing are always more expensive because they don't depend on all of the usual trim and covering devices which are used to hide poor workmanship. It's ironic, but true that "less is more" is usually more expensive than "more is more", since much higher skill and workmanship is always required.