[Costco] OFF! Mosquito Lamp 2 Pack $4.99 After C51 Cashback (Reg $21.99) In Store Deal Until May 30!!! YMMV!
C51 (Checkout 51) you get $12 cashback with each purchase. After factoring in the cashback you'll pay $4.99 for the 2 pack ($2.50 each lamp).
If you want 4 lamps, you can buy 2 of the 2 packs and pay only $3.99/two pack ($1.99/each lamp) because of the C51 bonus offer: get 2 claims approved with the OFF icon by Wednesday and get a bonus $2 cashback. Claim up to a max of 5 times (you only receive the $2 bonus once though)
See images for details.
YMMV since C51 cashback offers can vary (cashback amounts sometimes differs on different accounts)