The answer is: it depends. It’s generally difficult to get the gift cards for less than a 5% discount unless you stack discount methods.
For example, there are several people on the boards who stack the sam’s club discount, which is around 3%, with a cashback offer via an app plus bonus cashback with their credit card. However, you have to know when the app has the offer, and when the credit card has the bonus offer, and when they coincide to get the maximum discount. Oh, and a Sam’s membership.
The simplest discount is through a Target redcard, which comes as a credit card or debit card. It’s a straight 5% discount.
I feel like this BJs discount is pretty straightforward, you just need to use a credit card that has 2% or greater cashback for BJs purchases to bump it up over Target’s discount. That’s about as complicated as I’m willing to get seeking discounted GCs.
If you search the forums for gift cards, a bunch of threads regarding the more complicated deals should pop up.