Target is definitely the easiest.
If you have a BJs Club membership, they are usually 4% off and they often will run 6% off Disney gift cards during Black Friday. The reason you'd want to buy from BJs is you can combine it with credit card cash back (example: Discover and Chase Freedom are offering 5% back on $1500 in purchases via a digital wallet like Apple Pay for Discover and PayPal for Chase Freedom for the 4th quarter Oct-Dec). If you have both, you could get $3000 in DGCs for at least 4% + 5% back which equals roughly 8.8% off. Combine with cashback and you can get even more.
RetailMeNot also is offering 10% Cashback at
shopDisney, you can buy a $500 Disney eGift Card and in roughly 3 months, RMN will give you $50 back. The max you can get back per transaction is $50 though. The 10% cashback has been going on for a few days now, it may expire at any moment, but you should be able to do a few transactions and get $50 per transaction, up to 7 per month. Technically gift card purchases from RetailMeNot are excluded, so Your Mileage May Vary (YMMV).