See if you can find a used Beyerdynamic DT48 inexpensively. They're wonderful with cellonand other acoustic instruments. I've found three pairs between $60 and $100 or so. For the price, nothing touches the DT48. It's better than many more expensive headphones, as well.
You might want to consider a couple of other standbys, the AKG K-501 and the Sennheiser HD-600. The K-501 has a wondeful, organic sound and is "right" with an orchestra. It has a terrific soundstage, as well. The HD-600 is great with just about anything you throw at it, but it doesn't have the acoustic magic that the DT48 and K-501 have.
If you want to go further up the price range, you'd appreciate the HD-800, K-1000, HP-1000 and most of the electrostats.
And if speakers interest you, go for electrostats, ribbons, planars, or AMTs. I've owned all of those except planars, and they're fantastic with cello and other acoustic instruments. I've heard a few planars (Magnepans) and they all share the same magic.