Birch is a durable wood and has a hardness rating of 1260. Hard Maple has a hardness rating of 1450. They are similar in that respect. Both will most likely be a 'paint grade' , so called because there are patterns in the wood that would be undesirable for a clear finish but doesn't affect the durability of the wood. The cost of the wood is dependent on market conditions, the millers charges, trucking charges, and grade of wood. (Redwood prices skyrocketed when nature groups protected the owls that nest in them. It didn't mean that all of a sudden Redwood was a better wood because it cost more.) The grade of wood doesn't mean it is inferior, it has more to do with the patterns in the wood.