Thanks for the hits peeps! I had been using Crown because of its competitive pricing but I know it's not a top tier fuel. That's why I was looking at an additive. It's cheaper than Shell and other top tiers, to use a less expensive fuel and add the detergent.
I will however, consider Costco and check their prices.
I've seen Shell dispense at almost dollar more per gallon than what I'm purchasing. Even with the Giant points discount, it is still ridiculously more expensive.