The first digit is “5″ for US$, and “6″ for CAN$, followed by the price.
5 $ US 6 $ Canada 4 $ New Zealand 3 $ Australia 0 & 1 British pounds
51995 = $19.95USD | 61450 = $14.50CAN
If you don’t want a price, just use the default value (9000) – this will add a second smaller barcode embedded with “no price”. OR delete the 90000 and leave it blank, to get just the single barcode with the ISBN.