There is an excellent site for finding books at competitive prices and the range is amazing. Try ABEBOOKS, There are often sets of Child on there, it is always worth a look as the stock changes with great rapidity
Dont knock the 1854 edition of British Ballads as there are many songs in there that are not in the 1884 edition.
The last volume ,10, was published much later and is often missing.
I got my 4 vol Bronson and 2 vol Sharp Folk songs of England from there and both have been very useful in giving versions of the songs to my friends
Good Hunting
Old Nic
Young No More