On my last trip my girlfriend and I took a road trip to Cartago and ate at La Casona de Cartago. She had a filet that was very good and I had the mixed grill which was a lot of food, I was hungry and invited our driver in to eat, but even so the 2 of us could not finish the Medium Plate. The tomato soup was very good as well. It was a little pricey but I felt it was worth it, I do not remember what the bill was but I want to say it was close to $70.00 for 3 people but I only had 1 beer and we all had cokes. You can check out the menu on their site but the prices are not posted.
http://www.lacasonadecartago.com/