This sounds like an Advance Auto deal. I have done this a couple times for batteries. They typically have good coupons available.The coil pack went out on my wife's Taurus. I drove it to Advance Auto and had them put it on the machine to check it and they confirmed it was the coil pack.
The guy looked it up and said they had it in stock. I asked him the part number while standing at the counter. He gave me the part number and I ordered it online to be picked up at the same store I was standing in. I googled coupon codes before the order and got a 20% off code.
I placed the order with code and within five minutes it popped up on his computer. He was really cool about it and even said he was going to do the same thing since his discount was less than that. IIRC is was a savings of $17.