Chances are that your mother already has a copy of this vintage cookbook.
Betty Crocker's infamous "Pie Cover" Cookbook is one of the most commonly found books in the field. I consistently find it at estate sales, garage sales, church sales, library sales and in bookstores, and more importantly, it consistently sells in the $50 range.
Condition is obviously a premium on most cookbooks, especially well-loved and often used ones like this one, published by The Golden Press in the early 70's and featuring over 1600 recipes.
The book can be found in a hardcover format or 3-ring binder format (view here). The best way to identify it is the circular, pie-wedge style of the front cover. There are many comparable copies with a rectangular illustration, which do not command the same price. Make sure that there are no missing pages and that you describe any dampstaining in your item description, and you will see this book sell anywhere from $39.95 to $75. I will also add that I once came across a shrinkwrapped copy of the original edition which sold for $200 via Amazon last year.