The Washington Civil War Association is sponsoring the 10th annual Battle of Spokane Falls and Civil War Reenactment Weekend with living history demonstrations at Riverside State Park (Equestrian Area). This event will be held Memorial Day Weekend, Saturday through Monday, May 23rd through the 25th. Although I couldn't find admission prices, last year's admission was $7.00 per adult; those 12 and under were free. I imagine prices will be similar to last year.
For hours, schedule of events, directions, and more details, click here.