Some states also have reciprocity agreements with adjacent states (and in at least one instance, a nearby Canadian province) that allow reduced tuition and don't depend on choice of majors.
For instance, Minnesota residents can attend U Wisconsin-Madison for about $12k a year under the normal rate for out of state residents.
Other undergrad, grad and professional school reciprocity agreements between those states are here:
MN-WI Tuition Reciprocity College Prices
Minnesota also charges instate tuition rates for students from: North Dakota, South Dakota, and Manitoba.
Tuition Rates, Reciprocity