This is actually pretty easy. I'm surprised (shocked actually) more haven't chosen this, but several have got it "right"---a +1 for a Colt Single Action Army with military (US) markings, 7.5" "Cavalry" especially. Do it right and if/when needed you could pay for a good part of your kid's college (including out of state, etc) with one of these. In the meantime, one heck of a conversation piece. As someone else said, better yet make it two of 'em, if "allowed" under the OP's unstated rules, or a crate of them.
Same as above goes for those that have said 1851 Navy and Colt Walker--they got it right too! Have you seen what a "as new" for any of the above Colts fetches?!--that's when very rarely found.