Here's where to shop for low-cost groceries delivered to your door

Maybe you really hate grocery shopping or maybe you're really, really busy. Thankfully, there are a growing number of online grocery delivery services that will do the heavy lifting for you.

But how much extra are you paying for that convenience and which service actually provides the most value?

To find out, CNBC Make It compared prices listed online from Amazon Prime Now, FreshDirect, Instacart and Postmates for delivery in the greater New York City area. We crunched the numbers on 25 everyday grocery items, looking at a mix of national brands and each retailer's store brands, as well as both organic and traditional products.

It turns out Amazon's relatively new service, Prime Now, is the one to beat when it comes to price. Prime Now, which generally sources groceries from local Whole Foods stores, was the cheapest option in the most categories where all four retailers sold a similar product.

Here's an in-depth look at the four delivery services, from least to most expensive:

• Upfront cost: Included in Prime membership ($119/year)
• Delivery Fee: Free for 2-hour delivery on orders over $35, otherwise starts at $4.99
• Delivery availability: 1-hour and 2-hour delivery windows available in 88 major metros across the U.S.

If you have an Amazon Prime membership, it pays to have your groceries delivered via Prime Now, as opposed to the other services we analyzed. The total for 25 products purchased from a nearby Whole Foods came to $83. And Prime Now offered the least expensive option in 15 of the 25 categories when comparing the unit price of each product.

Of course, your options may be limited to products sold by Whole Foods. If you're looking for Dixie paper plates or Tide laundry detergent, for example, you'll need to substitute for the grocery chain's more eco-friendly products that may be sold at slightly higher prices.

To access this online grocery delivery service, you do have to be a Prime member — which comes out to be roughly $10 a month. Prime membership not only gives you access to grocery delivery, but also to Amazon's ever-expanding entertainment options and free 2-day shipping.

• Upfront cost: $0 for regular service, $99 annual fee for Instacart Express membership
• Delivery fee: $3.99 fee for same-day deliveries of $35 or more, Instacart Express customers get free deliveries on orders over $35
• Delivery availability: Same-day delivery available for 20,000 stores across more than 5,500 cities in the U.S. — including all 50 states and Washington D.C. — and Canada

When it comes to delivery, Instacart has the widest footprint of the services we surveyed, covering metros in all 50 states. And unlike Prime Now's limited grocery partners, Instacart is available through more than 300 retailers, including ALDI, Costco, Publix, ShopRite and Wegmans.

Because it partners with so many retailers, the prices can vary. However, CNBC Make It compared the delivery prices from Instacart for both Acme and ShopRite in Northern New Jersey. Both retailers state that the food costs on Instacart are higher than in-store prices.

Between the two supermarkets, a cart full of the 25 items we selected at ShopRite came out to $85, about $8 less than a virtually identical cart from Acme. (The prices listed in the table above reflect ShopRite prices.)

• Upfront cost: $0 for regular service, $129 a year for DeliveryPass membership
• Delivery fee: $5.99 to $7.99, depending on location, DeliveryPass customers get unlimited free delivery
• Delivery availability: Next-day delivery available for almost 30 counties throughout Connecticut, Delaware, New Jersey, New York, Pennsylvania and Washington D.C.

FreshDirect operates slightly differently than Prime Now or Instacart. Instead of having a shopper pick out your items at a physical grocery store, FreshDirect ships them directly from its warehouse. But that doesn't save you money, as it turns out. The 25 grocery items we shopped totaled just under $103, about $20 more than an almost identical order from Amazon Prime Now.

Beyond the price of groceries, FreshDirect may not be great for small, last-minute orders. You need to order a minimum of $30 to get your groceries delivered and delivery windows generally start the following day. And while the company does not charge any service fees, it does include a nominal fuel surcharge on each delivery.

• Upfront cost: $0, $99.99 a year for Postmates Unlimited
• Delivery fee: $2.99, Postmates Unlimited customers get free delivery on orders over $15
• Delivery availability: San Francisco, Los Angeles, and New York

Postmates' Fresh service is the most limited option of the services we tried, available in just three major cities according to the company's website. Not only is delivery limited, the East Village-based grocery store filling the order only had 18 of the 25 required items.

Plus the mark-ups through Postmates are ridiculously high. A package of 365 Everyday Value unsalted butter through Prime Now is $3.49, while the same size package of Organic Valley unsalted cultured butter sells for $11.79 on Postmates.

Postmates doesn't charge a delivery fee for the $100 order, but the online grocer does tack on a service fee of almost $18. In the end, Postmates Fresh is too limited and too expensive for most customers to get a lot of value out of this service.

Don't miss: Here are all the ways you can buy groceries on Amazon—and how much each costs

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