Which type of push lawn mower do you think is least expensive to buy and operate? Gas, corded electric or cordless? You're right if you said a corded electric. Consumer Reports' top-rated corded models cost about the same as gasoline-powered push mowers, around $200. (Consider the Black & Decker MM875, $240.) And they're less expensive to operate.
With gas prices at roughly $4 a gallon, figure on saving $10 to $20 a season mowing a quarter acre with a corded electric. The savings are even greater if you factor in the cost of maintaining a gas mower, which unlike an electric model, requires oil, filter and spark plug changes. Corded-electric mowers are also quieter and create no exhaust emissions (other than those from the electric company). The downside, of course, is that you have to deal with the cord, making corded electrics best for mowing no farther than 100 feet from a power outlet.
Cordless, battery-powered models use little energy. But they're about twice the price of corded-electrics and gas-powered mowers (our top-rated Black & Decker CM1936 costs $400). On top of that, you typically have to replace the battery every three to five years, at a cost of around $100, making cordless models the most expensive of the bunch overall. And batteries have limited run time (about 45 minutes max). So, as with corded models, cordless mowers are not ideal for large lawns.
Of course the least expensive of all is the push reel mower, the kind your parents or grandparents may have used. Unfortunately, they don't have the cut quality of a power mower. And they're not practical for large lawns or if you let the grass grow too tall. Still, the Fiskars Momentum did relatively well in our mowing tests and, at $200, is in the same ballpark as gas push mowers and corded electrics. Maybe best of all, push reel mowers create zero emissions, and you get to listen to the birds as you mow. (You can always keep the old powered mower on standby, in case the lawn gets out of hand.)