First, nothing is as good as a fresh-from-the-package new blade. But I have the Grace Company Tru Sharp electric sharpener and it does an okay job. Of course you could buy quite a few new blades for the cost so if you want to try it, wait until JoAnns has a 50% coupon.
I also found 5 packs of blades at Walmart online for under $20(in the US.)