The first film achieved alot more than its budet would imply. They saved alot because GM sponsored the cars, and Michael Bay cut his director's fees. They also used the CGI scenes sparingly, probably why most of Prime vs Megs & Bumblebee vs Barricade was offscreen.
didnt they get alot of funding from the military as well? michael bay had alot of connections with the military, but since transformers was a huge success, they have to have a bigger budget movie to add cooler fight scenes