"Solid Gold" is not a real term that makes a lot of sense in your regards.
Solid Gold itself (24 karrot) is very soft and pliable material. Nobody uses "solid gold" because of the weight and pliability, especially in jewellery or watches
I've seen the 18k gold number used, so what that means is that of your Gold, lets say 2oz of Gold, that means that it is 18/24ths pure gold, or only 75% gold, or roughly 1.5oz of actual gold.
but thats also neither here nor there. if the estimated total weight of the entire watch body is 2oz (Pebble steel, Moto360 and samsung gear range from 1.9 to 2.3oz), that is total body weight including the mechanics, non gold portions and internals. In all likelihod, there is probably well under 1 oz of gold per watch. I'm willing to bet there's probably not more than $500 worth of gold actually used.