Walmart offers the Champion 3,100-watt Portable Inverter Generator for $581. Choose in-store pickup to drop it to $566. (For Prime members only, Amazon charges the same.) That's $75 under our mention from two weeks ago and the lowest price we've seen. (It's the best deal now by $209.) It features a 3,100-watt max output (2,800-watt rated) and can run up to eight hours on a full tank of gas.