Costco is offering synthetic oil changes again for $39.99 ($10 off). This is valid for up to 5L. This is nationwide across all locations, but bare in mind that not all Costco locations have oil change services.
I’d recommend phoning your local store before heading down to be sure if you’ve never used the service there before. These sales typically last one week long.
If you don’t do your own oil changes this is worth a look. It’s also worth noting that certain Costco locations only do synthetic oil changes. Welcome to Costco Wholesale