It is a Mansfield and Lamb and comes with a scabbard and that brass sword hanger doohicke, but the hilt… The pommel has that patchwork appearance of brass that has been over-cleaned with a strong chemical sometime in the past and I don't like that green oxidation on the quillon. It looks like thing have dripped onto the brass of the hilt and that number on the pommel might mean the pommel has been removed from the blade at one time. You should probably remove the yellow stuff from the blade.
So, you have a real sword with scabbard and hanger. A dealer may ask for more based on a Mansfield and Lamb sword being assembled in America of American made parts, but the company did deliver 37,508 by the end of it contracts so it is not a rare sword. The hilt has issues. If we look at Thillmann's book, he has Mansfield and Lamb's last two contracts as dated June, 1864, for 8,000 sabers and January, 1865, for 5,000 sabers. If the sword you're looking at was from the last batch it never made it to the circus, let alone saw the elephant. And a sword that saw the elephant is really what you want from a Civil War sword.