Competition is heating up in the grocery industry.

Amazon's recent acquisition of Whole Foods and the subsequent price reductions have led customers to question if the chain — which had earned the moniker "Whole Paycheck" — truly provides significant savings or if it's just as expensive as ever.

For members of Costco, which has long been a secret weapon for customers aiming to cut down their grocery bills, the wholesale club still seems to be the better bargain. Recent data from JPMorgan found that Costco remains a "whopping" 58 percent cheaper than Whole Foods on a per-unit basis for groceries.

"[Costco] offers an unquestioned value prop with the best pricing, curated assortment, strong private label offering, and treasure hunt atmosphere," JPMorgan analyst Christopher Horvers wrote in a note to clients, as reported by CNBC.