Print and digital may have found the ideal place to coexist: the comic book industry.

A report released last week estimates that North American sales of comics — whether single issues, collected editions or digital downloads — were $870 million for 2013, up from $635 million in 2012. Digital sales rose to $90 million from $70 million. That strong demand for digital is welcome news for the entrepreneurial writers and artists who are continuing to evolve their digital portfolios.

In April, Thrillbent, a website for free digital comics that began in 2012, rolled out a $3.99 per month subscription model. The site was developed by Mark Waid, a popular comic book writer, John Rogers, a television writer and producer, and Lori Matsumoto, the major-domo.

“We’ve been really good at doing what I’ve been wanting to do,” Mr. Waid said, “creating a situation where we can provide content and fans can pay a fair price for it.”

Thrillbent’s subscription model will help provide stability for its creators and consumers, Mr. Waid said, and help the site take its next step: moving beyond comics by him and his friends and bringing in writers like the science fiction author Seanan McGuire, who come with their own considerable audience.