Official goldback.com exchange rate for 08/31/2023 remains $4.06 as it has not been updated since 8/29/23.
After a review of online sellers' prices, the best price for an in-stock 1 Goldback is $3.71 over at Defy The Grid
https://defythegrid.com/product-category/gold/aurum/goldbacks
The best price for an in-stock 50 Goldback is $177.64 @APMEX