Value of mint condition first pressing of Sgt. Pepper?

I have a mint condition first pressing (I think) copy of Sgt. Pepper's Lonely Hearts Club Band.  Vinyl is shiny and plays flawlessly, jacket is shiny with few indentations, and insert looks like new.  Any idea how much it might be worth.  Also, any idea as to how much value something like this gains over the years?  I'm thinking of giving it to my granddaughter (age 4) for her to cash in when she graduates high school.
Any input will be greatly valued.Russ