I recently bought a Phottix Geo One for around €100. It comes with 3 or 4 different cables to connect the unitto a wide range of cameras, including obviously the D600. In addition, it comes with a wired remote which you have to plug directly into the GPS unit.
It is well built, on par with Nikon unit.
I have not really tested it in the field but I will be on a 2-week trip to Thailand next week and will be happy to report my experience.
So far, I tested it indoor in my flat (not best conditions as GPS do not work well indoor) and geo-tagged one picture: it was off by nearly 50m. We'll see if it performs better outdoor. Anyway, I do not need something perfect...