A good way I've found to make calibration targets is to have them printed on foam board by a vendor like Vistaprint. For example, they offer foam board prints like these for fairly cheap - an 11"x17" board for about $20USD. The benefit here, is that the printing process is likely better than whatever inkjet printer is in the office, and the foam board itself is much less likely to warp or bend like a piece of paper. Overall, I think it's a good balance of quality and price.
To generate the print image, I used the Calib.io pattern generator (which they kindly offer) to recreate the standard OpenCV 6x9 vertex checkerboard with 30mm squares on an 11"x17" (279.4mm x 431.8mm) surface. I used that output (converted to .png) as the print for the foam board. Viola!
Here is the print for the OpenCV 30mm checkerboard:
Here's a picture of the calibration target after it arrived:
And a close measurement with the calipers to verify 30mm:
A reader with a keen eye will notice in the caliper measurement picture that the corners are not exactly aligned, and the edges are not perfectly sharp - both I guess are due to normal tolerances and imperfections in the printing process. But, for $20USD, it's a target that is light weight, rigid, and relatively well-printed.
For applications that need very high precision, more complex target configurations, or heavy duty mounting, I'd suggesting taking a closer look at Calib.io. They offer all kinds of metal-backed custom targets, along with mounting solutions and even calibration software.
Hope this is helpful!
Happy calibrating 
