Marianne Gries enters Whole Foods Market in Bedford with a determined look in her eye. She is not here to browse or squeeze the Charmin. The 37-year-old director of a small nonprofit in Lowell has an agenda: getting out of this notoriously pricey supermarket for $20 or less.

She makes a beeline for the bulk food aisle, where she scoops up organic lentils and grains from large bins, weighs them, bags them, and pays an estimated 50 percent less than if she bought prepackaged versions in other aisles. She finds quinoa, a grain that can sell for more than $7 a pound, for $3.69. She snaps up small-batch roasted coffee for $4 a pound less than it costs on the shelf.

Her total at checkout: $16.70.

Buying in bulk is just one way in which Gries manages to live fabulously, yet frugally. She surveys grocery store websites to find the best sales, buys second hand, and, when she can, does it herself, such as knitting the Shetland wool shawl draped around her shoulders. She still enjoys the finer things, like a night out at a restaurant. She just doesn’t pay full price.

“Your attitude changes when you look at money as a tool to improve your life,’’ she said. “I think about how to use it to make the maximum impact.’’

Getting the most out of your money isn’t hard, says Gries. But it requires planning, monitoring, and discipline.

She begins with a spreadsheet, where she and her partner plug in their salaries and necessary expenditures such as rent, medical bills, and $150 every other month for hair maintenance. There’s also a line item for family fun.

The blueprint helps track their spending and pinpoints when and where they need to pull back. They review it weekly. “This way money is not a mystery,’’ says Gries. “Knowing you only have x amount to spend takes the anxiety of out of it.’’

Before they began tracking expenses, for example, they ate out four times a week, usually after a hard day’s work “when we were tired and cranky,’’ Gries said. They found they were spending a lot of money on something they weren’t enjoying. So they cut back on restaurant meals, cooked at home, and put their money toward weekend getaways to places like Bar Harbor, Maine.

When she does visit a restaurant, it’s usually with an online coupon from Groupon, Living Social, or Restaurant.com, websites offering daily deals and half-price gift certificates. Recently, she bought a $50 gift certificate to the Left Bank Restaurant in Tyngsborough for $25.