Estimating Equilibrium Price for Advertising using Simultaneous Equations Model
You're definately on the right track. What you are doing is estimating the inverse demand and inverse supply in your market. The variables Visits Print and Prod can be used as "shifters" i.e. instruments for the quantity in the equation in which they are not present. Visits can be used as an instrument for quantity, when estimating the inverse supply equation and Print and Prod can be used as instruments for quantity when estimationg the inverse demand equation. 

A well known example of how this works is Grady's article on Fulton fish market. You can find STATA code that replicates that article here: https://www.stata.com/data/s4poe/chap11.do .

The data sets for the stata code are here: http://www.principlesofeconometrics.com/poe4/data/stata/ .

Of course you should test the validity of the assumptions behind the use of IV in your SEM with the Hausman, Sargan-Wu and Stock-Yogo tests.