If you're talking about the sales ratio within a single restaurant, then you may be correct about 3:1 or 2:1--although certain places would certainly sell more DD, like Malnati's. But overall market share for deep dish in the Chicagoland area is nowhere near that high. I would truly be surprised if it commanded more than 5% of the overall market. I would even be surprised if it were more than 2 or 3%. It is an oddity--yes, a delicious, indigenous-to-Chicago oddity--but an oddity nonetheless.
As for price, all good pizza in the Chicago area is "expensive." I put that in quotes because I think it is appropriately priced. A 15" thin crust with two toppings should be $20. Pizza is not fast food. You're not supposed to get a pizza for $11.99. Anything less than approaching twenty bucks should be suspect.