Instant bitcoins — at a price

A Liberty Teller bitcoin machine was placed in South Station in February 2014.Essdras M Suarez/ Globe Staff/file

One of the two ATMs in the Dorchester check cashing shop was just what you’d expect — one of those squat, grimy machines that charges you a fee for access to your own money, no matter where you bank.

But the other ATM was something else — tall, gleaming white, with that new-electronics smell and a big touch-sensitive screen. This one also doesn’t care where you bank or even if you have a bank account. And it doesn’t spit out $20 bills — it gobbles them up. A second or so later, your smartphone chimes and vibrates, confirming the money you just fed to the machine has been transformed into bitcoins — the computer-generated currency that’s lately become one of the world’s hottest investments.

Care to roll the dice and hop onto the bitcoin bandwagon? An ATM is probably the simplest way. Too bad it’s also probably the most expensive way. So maybe we should expect to find them in check-cashing shops, where people are probably spending more than they should for financial services.

I first wrote about bitcoin ATMs three years ago, when one of the first such machines showed up where you would expect, in the South Station train terminal. There it beckoned to thousands of affluent commuters with enough spare capital to take a flier on bitcoin.

But the South Station ATM is long gone. Perhaps it was the plunging value of bitcoin in those years. Worth around $1,200 in late 2013, it fell below $200 by early 2015.

Today it’s a different story, with bitcoins trading at around $2,600, and other so-called cryptocurrencies like Ether also surging in value. So you might expect to find bitcoin ATMs popping up all over Boston’s Financial District.

Instead, they’re at places like the All Checks Cashed currency exchange on Washington Street, next to a cut-rate cellphone store and down the street from a laundromat. Or at a convenience store on Mass. Ave., or a gas station in Cambridge. According to Coin ATM Radar, a site that tracks such things, there are eight of them in Greater Boston, and more than 800 in the United States. And around here, nearly all are in the low-rent districts.

But why? In the eight years since the alternative currency was created, hardly any retailers have stepped up to accept it. So why are bitcoin ATMs popping up in gas stations and convenience stores?

For shopkeepers like Khan Mohiuddin, owner of the Happy Superette convenience store in Dorchester, it’s simple. That bitcoin ATM brings in some extra cash. “I don’t know how that machine works, but I get $300 rent a month,” he said. But Mohiuddin said he’s seen only a few customers use it.

The owner of All Checks Cashed could not be reached for comment. But Marc Grens, president of the Chicago-based bitcoin ATM operator Digital Mint, said his company targets consumers who rely on cash, rather than savings accounts or credit cards. “We see some of the underbanked customers using this,” he said. “Any new market, you go where the most pent-up demand is.”

A pent-up demand for bitcoin among people who can’t even write checks? It seems incredible, but Digital Mint has deployed more than 50 ATMs in 10 states. And while Grens won’t reveal a customer count, he insists that people use them.

Some buyers, he says, shop at the few retailers who accept bitcoins, like Gyft.com, which sells gift cards, or the travel site Expedia.com. Others are small business owners who buy merchandise from overseas from suppliers who want to avoid bank transfer fees. And of course, some are speculators.

If Grens is right, it suggests that low-income Americans are more financially sophisticated than we realize. That jibes with the research of University of Pennsylvania professor Lisa Servon, whose recent book, “The Unbanking of America,” claims that the users of check cashing shops often prefer them to traditional banks, because they offer faster access to their money.

Sure enough, a bitcoin ATM often delivers its goods faster than an account with an online bitcoin seller like Coinbase, which can make a buyer wait for several days.

Still, buying bitcoins through an ATM is pretty complicated. Hours before I set foot in the store, I downloaded a bitcoin wallet app to my Android phone. This piece of software houses the digital key that gives you access to your digital currency. I opted for a free app called Blockchain.

Some criminals have used bitcoin ATMs to launder their booty. The machine I used requested that I scan my driver’s license before proceeding, so I can’t hide. It also got my cellphone number and sent a text message for a further identity check.

After the machine provided the digital code to track my transaction, I started feeding it cash — $20. But since they’re going for about $2,600 a piece, I ended up owning just a tiny fraction of one bitcoin.

But 16 percent of my purchase was eaten up in fees. Just like that, my $20 was suddenly worth about $16.80. Three years ago, when I first purchased bitcoin on a desktop computer, the fees were negligible. What the heck happened?

Grens blamed the growing cost of running the global bitcoin network as the currency’s popularity soars. Even bitcoin purchases made over the Internet cost more than they used to; the popular site Coinbase charges $1.49 for a $20 purchase from a bank account, or about 7.5 percent.

With the ATMs you’re also paying for those clever machines, and the rent that goes to each shopkeeper. It adds up to a fat slice of your original investment. And so it only makes sense to buy bitcoins this way, if it’s the only way you’ve got.