Here are just two examples of how you might include a cool rocking chair in a modern design setting. Both photos are from the Swedish magazine, Skona Hem, which is full of cool modern homes. The rocking chair in the top photo is a bit more traditional looking, while the Eames chair in the bottom photo has all the modern credentials!
Wright auction in Chicago, off an auction estimate of $200 - $300. I love the simple design in birch and iron with an upholstered seat. This is Danish circa 1950.
Here is just one example of a Charles and Ray Eames rocking chair that sold at a Christie's auction for $3,325 off an auction estimate of $1,500 - $2,000. These are highly desirable, and the price at auction will no doubt depend on who's bidding on the day and the condition. I've seen them go for less and more.
I love this Fritz Henningsen rocking chair, circa 1930's. It's a very comfy looking rocker, with wonderful modern appeal. Fritz Henningsen is highly collectible, and adds instant modern credentials to your decor. This sold for $8,750 at a Sotheby's auction off an auction estimate of $10,000 - $15,000.
Gae Aulenti is another highly desirable Italian designer. The curves on this 'Scarsgul' chair designed in 1962 add so much interest to the chair. It becomes a work of art in a room, but looks comfortable too! It's made of laminated and ebonized wood with leather upholstery, and sold at a Christie's auction for $1,500 off an estimate of $2,000 - $2,500.
Bonhams auction for $488. It's described as 3rd quarter 20th century. The design of the rocker legs make it. Looks inspired by a Thonet.
Rocking chairs can be very modern cool. Pick one with lots of curves, or with simple lines like the Eames version. They are fun design elements, and rocking while reading a good book can be very calming.