I've been looking for a '56 Mantle for over 15 years to complete a set I've been working on as a kid.
The price has always been an issue (over $1,000) at crd shows, and you have to be careful of fake ones.
After doing lots of research, I knew a PSA 6 '56 Mantle was the way to go. First, you know it's a real Mantle card. The one I bought was under $1,000, has WONDERFUL centering, crisp colors, and solid corners. It is now the center piece of my complete '56 set.
There are PLENTY of Mantle's on E-bay, and some sellers are willing to work with you on price. Do your research and shop around. You;ll find the one that is right for you.