$14 $20
Amazon has the Calculated Industries Center Mark Drywall Recessed Lighting Cutout Magnetic Locator (8110) for $14 with free shipping on $25+ or with Prime. Fits 4", 5", 6" recessed (non-LED) can light fixtures, and includes two magnetic targets.
Comments & Reviews (1)
Would be even easier if it came with 4", 5", and 6" discs that fit over the puck to trace the hole, but those wouldn't be hard to DIY make out of a plastic can lid, wood, or whatever.
Thank you!