Your fridge is bare. You're strapped for time, and the thought of taking the kids to the supermarket is exhausting.

Grocery delivery services are finding their niche.

Julia Moon, a mother of 1-year-old twin boys, can appreciate grocery delivery.

"All I have to do is get on a computer and open a door, and I have my groceries for the week," she said.

Moon agreed to help check out three popular delivery services -- Instacart, Shipt and Amazon Prime Now.

While her boys napped, she shopped -- putting the same groceries into each cart.

Instacart and Shipt will shop at various stores, so Moon directed them to shop at her neighborhood H-E-B.

Within seconds of placing her Instacart order, Moon got a text message indicating her shopper was on the job.

"Instacart does a really good job of keeping you informed of progress or delivery," Moon said.

All three deliveries were prompt.

Amazon Prime Now was at the doorstep within 35 minutes of placing the order. Instacart delivered in about an hour. Shipt made its promised window between noon and 1 p.m.

When it came to the quality of the produce, Moon got a mixed bag.

Shipt delivered near-perfect Fuji apples, avocados and bananas.

"The overall quality of the produce was good," Moon said.

But half of the bananas from Instacart were bruised, and Amazon delivered soft, overripe avocados and a bag of visibly bruised apples.

As for prices, each item does cost more than if Moon had gone to the store herself. For example, a can of Progresso chicken and noodle soup that was $1.88 at H-E-B cost 26 cents more from Instacart, 31 cents more from Amazon Prime Now and 41 cents more from Shipt.

It adds up.

For a dozen items that total $38.18 at H-E-B, they cost between 14 and 17.5 percent more when purchased through the delivery services. Shipt was the most expensive for the items Moon ordered.

For busy moms like Moon, having diapers delivered to the doorstep is a huge help. For her boys' Pampers, Instacart charged 14 percent more than the store price, Shipt charged 18 percent more and Amazon Prime Now charged 28 percent more.

There are other costs, too.

Instacart offers a free trial; otherwise, a regular delivery fee for orders more than $35 is $5.99, and one-hour delivery is $7.99

The service also offers an express membership service that runs $14.99 a month, a money-saver for frequent users.

Instacart also charges a 10 percent service fee.

Shipt requires users to sign up for a membership which costs $14 per month, or $99 per year. The membership includes free delivery for orders more than $35. First-time customers get a $15 credit, and a tip is recommended.

Amazon Prime Now offers free two-hour delivery as part of the annual $99 Prime membership. If you want your groceries in less than an hour, the fee is $7.99. There may also be a "rush hour" fee of $4.99.

All of the services offer some kind of sales or coupons to help users save money.

Grocery delivery may be the greatest thing since sliced bread, but it's a convenience with a cost.

"Being a mom of twins, busy every day, it's super convenient. It makes my life a whole lot easier," Moon said. "Once you add up all the fees and prices, is it worth it? I don't know."