Another option, if the print is valuable, is plastic plumbing tube. Shipping cost with obviously be higher. But some types of the plumbing tube are much lighter than others, so perhaps not too bad. You could glue a cap at one end and tape the cap at the other. Or use a screw cap (with tape) at one end. Though the carpet tube that Ian suggested tends to be very strong.
Also, the triangular "tubes" that FedEx and the USPS offer would have an effective diameter of about 3 to 4 inches.