[quidnunc]

Go to www.alibris.com

They sell used and rare books and you might be able to look up similar volumes of the same titles to get some rough idea.

[fqued]

The 1885 Memoirs alone aren't worth much (you can buy a copy for under $50.00), BUT,
if the signature of Grant is a real signature, and not printed, that raises the value quite substantially. Check to see if it is a true signature, and not printed on the printing press.