ClassPass, the startup that lets you book gym classes at various locations for a flat monthly fee, has increased its cost from $125 per month to $190 per month for unlimited classes. New members will be charged $200 per month for unlimited classes.

To put that in perspective, ClassPass is now more expensive than a membership at the high-end gym Equinox. Those currently paying $125 per month will be enrolled in the plan that gives you 10 classes per month and will have the option to pay more for unlimited classes.

As you can imagine, ClassPass customers aren't happy.

My entire Twitter feed (which, yes, is mostly tech and media people living and working in New York or the west coast and hardly representative of the entire US population) is full of complaints. But it does highlight the broader challenge all those "Uber for X" companies face. You either have to reach a massive scale to keep costs low or raise prices. ClassPass decided to effectively double its prices from where they were about a year ago.

In a statement to Tech Insider, a ClassPass spokesperson said the price increase was necessary to keep a sustainable business.

"We’re encouraged by the usage on ClassPass and the tremendous growth we’ve had, but we have to be realistic about the economics to sustain it and are in the process of investing in the health of our business," the spokesperson said. "We are evolving our business model and adjusting prices in order to create long-term sustainability with both our members and the market. We are committed to having an unlimited product as affordable and accessible as possible, that still provides incredible value to our members while also growing and validating the industry as a whole."

And here's what some customers had to say:

And so on.

ClassPass has gotten great reviews, but it's tough to see how it's better than joining a "normal" gym that also offers unlimited classes.