Let $ x $ be the cost per square inch of gold paint, and let $ y $ be the cost per cubic inch of concrete. Since a 1 inch cube has surface area 6 $ \text{in}^2 $ and volume 1 $ \text{in}^3 $ its total price will be $ 6x+y $ dollars. Similarly, a 2 inch cube has surface area 24 $ \text{in}^2 $ and volume 8 $ \text{in}^3 $, so its total price will be $ 24x+8y $ dollars. We are given that \begin{align*} 6x+y &=\$ 1.30 \\ 24x+8y&= \$6.80 \end{align*} Subtracting 4 times the first equation from the second gives $ 4y=\$1.60$ , so $y=\$ 0.40 $. Hence $ 6x=\$0.90$ , so $x=\$ 0.15 $. Since a 3 inch cube has surface area 54 $ \text{in}^2 $ and volume 27 $ \text{in}^3 $, its total price will be a total of $ 54(\$0.15)+27(\$ 0.40)=\boxed{\$18.90}$.