Mac Pro with Thunderbolt Display 30 meters away
Copper-based Thunderbolt cables are limited to max length of 3 meters. Corning sells optical Thunderbolt cables you will need for the distance you specify here. You can get 10m lengths at Amazon for US$299. They come in 30m and 60m lengths for US$659 and US$1299, respectively. I haven't had the need for these lengths yet, but I did the research a few weeks ago for a project which didn't get off the ground.