If you want a strong, highly reflective item to use as a signal mirror, for zero cost, take apart one of your dead computer hard drives. The disk platters are highly polished and ridiculously reflective. And the physical disks themselves are very tough. You won't have an aiming aid, but the two-handed method works just fine. The first time I aimed one of these disks at my house, I though I was going to ignite the siding, it was so bright and cleanly focused.

While you're at it inside your dead hard drive, pull out the magnets too. Those are super strong rare earth magnets. Useful for many things.