Value of Chamber's Encyclopaedia

What is the value of a 12 volume set of the Students Handy Edition of Chambers' Encyclopaedia? I could not find a date on any page, but on the title page it states "with very large additions upon topics of special interest to American readers; and giving American statistics of population down to the census of 1890'. All 12 volumes are in very good condition and they belong to my mother who is trying to downsize. Thank you.

By Grace W.