GRM reported substantial gains (6hp iirc) with Magnacor plug wires and that is dyno testing before and after.
cheapest I've found them so far is $85 at http://www.ultrarev.com
You will not gain any hp if your wires are good to begin with. I don't think they necessarily "gained" but rather restored the power that was missing from the old wires.
I've had good luck with Arizona Autohauz. They have the cheapest prices and the great shipping and service. The do carry a lot of the factory brands like Mahl, Bosch, Febi, etc.