Value of 1929 Book of Knowledge Encyclopedia Set?

I have a 1929 Book of Knowledge, 20 volume set, with original bookshelf. The books are in excellent, little-used condition, with no damage. It has a green cloth hard cover with gold imprint. The volumes are slightly worn on bottom spine and corners from sitting on the shelf.

They were owned by an 83 year old woman whose father gave them to her when she was five years old.

What is it worth today to collectors?

By Mark from Toronto, Ontario, Canada