The ivory balls with numbers I've seen have been object balls. It may have been dyed at one time but the dye came off. A complete set of ivory pool balls is worth somewhere around $2000 and $6000, depending. An individual ivory ball might go for $40 to $500, depending.
On page 97 of the Stellingas' book on billiard collectibles is a picture of a set of ivory pool balls without color and small hand-engraved numbers. They value the complete set at $4000 even though the ivory is cheap and the balls are badly cracked. (Some of the prices in that book are a little high.) The set is said to be from about 1850.