Kvaser is indeed one of the good option available.
I am also presently looking for some cheap CAN Bus analyzer with DBC file support(not exactly CANOpen) . I found few Chinese variants but not sure if that will serve your needs, as the main problem will be with the PC software that is provided with them. Kvaser supports many good software like Vector/NeoSpy.
Anyway here is the link to what I found for CANOpen:http://www.aliexpress.com/store/product/USB-to-CAN-converter-with-CANopen-resolution-industrial-grade-isolation-Quaranteed-100/610023_537333916.html
If some time and budget is left - you can try this one to reduce the cost in future. As most of the time we don't need to use all the features of high end devices. But visa verse - high end tools are reliable and capable of debugging minute problems.