For example, on a recent episode of "Bethenny & Fredrik," the house-flipping duo is faced with renovating a kitchen counter. Eklund lusts after a Calacatta marble option, priced at $120 per square foot.
To educate Eklund that lookalike materials can save a ton of money, Frankel asks the salesperson, "Can you show us the side by side, porcelain to the marble?" After comparing the similar slabs of stone, Frankel asks for the price difference. The Calacatta they would need costs $30,000 to $40,000, while the porcelain was less than half that. (The pair compromised on more affordable stone.)
3. Stick to your budget
Frankel is also good at figuring out "how to get value out of something by using an economic approach and managing a budget," she tells StreetEasy.
The items that really break your budget, Frankel tells CNBC Make It, are not the big-ticket items. It's the little expenses that can really add up, so be sure to factor those into your total cost.
"When you really get jammed up is when you start buying ... towel rods and hooks and handles and all these little, annoying things. The things that cover your electrical switches, things that cover your electrical sockets," Frankel says.
"They really do add up. So the budget really has to be the whole budget."
Plus, Frankel uses any advantage she has to bargain. "I really don't pay full price for anything in design, because once you start doing multiple projects, you're using contractors and designers and tradesmen and tile and fabric companies, so I'm always trying to find a way to make it cost effective," Frankel tells CNBC Make It.
4. Use your leftovers
Another way Frankel gets the best look for little cost is a trick professional designers use — remnants. Leftover pieces of expensive materials are often on sale because of limited quantity. Or in Bethenny's case, she uses leftover materials from her own past projects.
For example, when decorating her Hamptons home, Frankel used extra wallpaper from her Tribeca apartment, according to People, as well as an Ikea mirror that she's had since her studio-apartment days. The money-savvy business mogul also reportedly used a "crappy old bench" leftover from the previous homeowners, and simply spray-painted it red.
Frankel also gets creative with cheap but impactful decor. Her Soho space featured artwork created by her then 6-year-old daughter Bryn, consisting of three large, colorful abstract paintings blown up and transposed onto canvas.