The cheapest way to purchase labels for your Brother QL printer is by buying once a re-usable cartridge for the label size you are using and then only purchasing new rolls of labels.
The following two labels are the most popular for library books and bus cards.
Brother DK-1209 - 1-1/7" x 2-3/7"
Label
https://www.officesmartlabels.com/brother-compatible-dk1209-without-cartridge-p/ofbro1209.htm
One Time Cartridge
https://www.officesmartlabels.com/Brother-Compatible-DK-1209-Reusable-Cartridge-p/ofbro1209c.htm
Brother DK-1201 - 1-1/7" x 3-1/2"
https://www.officesmartlabels.com/brother-compatible-dk1209-without-cartridge-p/ofbro1201.htm
https://www.officesmartlabels.com/Brother-Compatible-DK-1209-Reusable-Cartridge-p/ofbro1201c.htm
