The cheapest and simplest way is "do nothing". Even you kill them this year, the adult bugs can fly, they will lay eggs in your lawn next year. If your lawn is in good condition it can take it. Don't water July and August also helps because adult bugs look for moist soil to lay eggs.No eggs, no grubs. I found them in my lawn too, two pieces grass are dead. I replaced them this spring. After few good rains and fertilizer the smaller gap was closed by grass itself. They are grubs killer at store, you can use them in August if you really want to.
http://www.landscapeontario.com/howto/how-to39.pdf