Until 3pm, Oktoberfest is cheaper. See an overview over all lunch offers of the beer tents.
Since 1998 the word “Mittagswiesn” (Midday Oktoberfest) has not only been describing a state of relaxedness and bliss you can experience at the Oktoberfest around noon, but also a specific concept, to motivate more Oktoberfest visitors to come early. Between 10am and 3pm, the majority of showmen have special offers. Rides often charge the same prices as on the two family days.
In the past years, also most of the large beer tents adopted that concept, offering daily specials on their menus.