A penny saved is a penny earned - or something like that

Standing in line at the cafe to place my order. Two guys in front of me, a guy ordering and a guy waiting.

GO: I'll have a hamburger with a side of cheese
GW: Did you just ask for a burger with a *side* of cheese?
GO: Yeah, its cheaper that way.
GW: What?
GO: Its $1.69 for a hamburger and $1.99 for a cheeseburger, but a side of cheese is only 29 cents.
GW: Ah