As a reader discovered, Jegs offers the Autolite Platinum Spark Plug for $1.88. Add 15 to your cart for $28.20, then redeem this $15 mail-in rebate ($1 off each plug) for a final price of $13.20. With $6.99 for shipping, that's $1.35 per plug and the lowest price we could find for this quantity by $10. Each plug has a platinum ball design.
The rebate is valid for up to 16 plugs; however, buying more than 15 will raise shipping to $9.99, thus minimizing your savings. You can also bag free shipping on orders of $95 or more.