Calculators that predict near-term costs are far more practical. Most of us have no idea what installation of a home electric circuit panel should cost, so plugging your ZIP code and your preferences into a tool before getting bids is incredibly useful. Use it to throw out a bidder who's asking for the moon. I like both HomeAdvisor and Homewyse.com. (In Columbia, Mo., upgrading a panel costs $866-$1,224, Homewyse says.)  RedBeacon.com offers an even wider range of cost calculators for home services like landscaping or housecleaning.  The most useful estimator I found unmasks the mystery of the costs of auto repairs, offered by RepairPal.com. Not only does RepairPal offer ZIP-code level pricing—a water pump replacement should cost between $263 and $368 in north-suburban Seattle—it also offers additional necessary information, like this: Water pump repairs often require belt replacement, particularly if fluid leaked on the belts.  Getting a repair cost estimate takes only a moment, and it can save you hundreds at a repair shop.  "We have had consumers tell us that, after they showed a RepairPal estimate, a shop lowered their price," said Bret Bodas, director of RepairPal's automotive professional group. Not surprisingly, auto mechanics weren't thrilled about the tool when it was first made public several years ago.  But Bodas says fair pricing information helps honest mechanics, and the industry has slowly warmed to the idea of transparency. Napa Auto Parts actually licenses data from RepairPal for its own tool now.  (Read more: Why you shouldn't wait on frequent flier awards)  With both home and auto repairs, the data behind the calculator come mostly from cost estimation tools already used by contractors and repair shops. For example, automakers publish a list of labor times required for various repair jobs. Shops use those for estimates; RepairPal uses the same data, then adjusts for labor rates by ZIP codes, Bodas said.  Naturally, consumers with broken-down cars aren't always in a great bargaining position. Still, RepairPal can make sure you aren't being taken for a ride, and it can even suggest you might be better off paying to have a vehicle towed to another shop for a second opinion, if the first shop's quote price is wildly off the mark.  Sick consumers have even less bargaining power; for that reason, health-care cost calculators like the helpful one you'll find at FairHealthConsumer.org almost qualify as regret tools. Still, it's worth knowing what medical procedures should cost before having those conversations with your insurance company and your doctor's office.  And there are times when knowing you overpaid the dentist for your last crown gives you the power to pick a new dentist, so we'll call this a bargaining tool. And it's sometimes possible to negotiate price after the fact with providers; price comparison tools are useful in those discussions.  By the same logic, the various taxi price calculators are also helpful in real time. No, you can't get a cab driver to negotiate a metered trip. But before visiting any new city, it's worth visiting a site like TaxiFareFinder.com and plugging in various trips you expect to take. You'll get a map of your route and an expected cost, so you'll know if your driver makes an unexpected wrong turn, and you can demand an adjustment.  Predicting long-term future costs is fraught with peril; still, it's a good idea to know what you will be up against in 2020 so you can plan for the future. Before clicking on any of these sites, however, you might want to pour a nice cup of hot tea. They are likely to make your blood pressure rise.  There's plenty of tools for calculating the cost of children, in the near and far future. Let's start small, like they do. Uncle Sam offers his own tool at USDA.gov, where the first-year cost of a kid in the Northeast is pegged at about $14,000.  Look further into the future, and you may think twice about having a baby. Or at least about training that baby to be a scholarship athlete. BabyCenter.com thinks a child born in the Northeast today will cost $400,000 if she or he attends a private college.  If you dial up cost of college calculators, you will conclude that the BabyCenter number is low. At CollegeSavings.org, you'll get an even starker splash of reality. Assume 5 percent tuition inflation—and why not, that's how much colleges raise tuition each year at the moment—at a four-year private school will cost $316,000 by the time today's babies graduate. (That's just tuition—with room and board, the cost is $430,000!)  (Read more: New airline seats still put the squeeze on fliers)  Speaking of anxiety, you'll find hundreds of tools on investment sites offering to guesstimate how much money you will have, or will need, at retirement. Among the assumptions you'll see: average 12 percent market returns, spending levels remain at 80 percent after retirement, etc. You're already anxious enough.  Fortunately, here's one piece of pretty solid math. Every dollar you save today will be worth roughly $16 in about 30 years, if it's saved well. So the best way to ease your anxiety about all those big future costs is to use big data now to save money, and avoid getting ripped off.  —By Bob Sullivan, is an author and consumer reporter. Follow him on Facebook or Twitter @RedTapeChron.
Retailers use big data to maximize revenue—that is to take as much of your money as they can. Why shouldn't you have the same power?