Walmart offers the RoomMates Star Wars Classic Wall Decal Set for $10.73. Opt for in-store pickup to dodge the $5.99 shipping charge. That's the lowest total price we could find by $4, excluding the mention below. The set includes 30 decals.
A close price: Jo-Ann Fabric has it for $8.99 plus $1.99 for shipping via coupon code "SHIPH126".