When I got the opportunity I logged on to Amazon.com in search of the missing book and learned that, with the books no longer in print, my only hope of ever completing the set would be to buy a used book. I checked further and found that depending on which book, which edition, and the condition of the book of course, they ranged in price from 25 cents to well over ONE HUNDRED DOLLARS. Copies of the extremely rare number 39 can go for SEVERAL HUNDRED DOLLARS! My elusive number ten "glossy", that sold for 59 cents new, was selling for around $25.00.

Just out of curiosity I typed "Trixie Belden" into a search engine.

Trixie.com