BISMARCK, N.D. (AP) — North Dakota’s oil boom isn’t just driving up housing prices at the epicenter. Getting a roof overhead is getting more expensive throughout the state, with the average value of a home sold last year topping $200,000 — up more than 20 percent from 2011, a real estate trade group says.“Houses have appreciated statewide and inventory is low in the whole state,” said Jill Beck, CEO of the North Dakota Association of Realtors. “That comes as a shock to a lot of people.”North Dakota’s robust economy, led by its soaring oil production in the western part of the state, has resulted in record-high home prices and skyrocketing rental prices that reflect tight supply and strong demand statewide.