You won't get rich selling your copy. I did a quick search at ABEbooks.com:

Roberts, John S.
The Legendary Ballads of England and Scotland
London: Frederick Warne & Co. Full-Leather. Good/No Jacket. Very attractive leather-bound book. Undated but inscription on fep reads "Grandma from Robbie, Xmas 1879". Leather with gilt leaf design on edges of cover, and gilt page edges. Front and back cover have crack at spine
Bookseller Inventory #000093
Price: US$ 17.00


Ed: Roberts, John S:
The Legendary Ballads of England and Scotland
Warne, undated Hardback edition in original boards with gilt and black inlay to front board and spine. This is a very nice book. Slight bumping and rubbing to boards. Owner's inscription to f.e.p.
Bookseller Inventory #16901
Price: US$ 17.45


ROBERTS John S (compiled & edited by):
The Legendary Ballads of England and Scotland
(Frederick Warne [Chandos Classics] no date) Presents texts only - ie, no music - for a a good selection of traditional ballads, the result being similar to Percy's "Reliques". One of the Chandos Classics poetry series in brown binding, title colophons in gilt on front and spine, the latter being somewhat darkened. A little fraying at head. A couple of brown streaks appear at edge of first few pages, but overall quite clean for its evident age.
Bookseller Inventory #7194
Price: US$ 22.04

There are more like this, and the price tops out on the 15th copy:

ROBERTS,JOHN S. ed., Illustrated by b/w ills.
The Legendary Ballads Of England And Scotland
London: Frederick Warne & Co. 1868 12mo, pp628, The Chandos Poets series. NVG, full green leather, gilt spine, gilt Rugby School motif on front board, a.e.g., raised bands, lightly faded spine, light. shelfwear, book plate on front paste down, & previous owner inscription.
Bookseller Inventory #010916
Price: US$ 91.78