I'm going to agree that the single picture doesn't point to a $2k 1863 Sharps carbine. pictured below is an 1863 converted to .50-70 going for less from Dennis Fulmer.
To be brutally honest, unless I was supporting the museum, I'd pass and keep my eye out for a M1859 or spend some more for an M1863 or M1870 rifle. That said it might be worth giving them a lower price and see if they will take it.
As someone who works at a museum we do a lot of horse trading and our funds are tight… if they're selling to buy something else or to raise needed funds for building repairs they might bite.
Good luck and post some pics of whatever you opt to do. Ultimately, it's what makes you happy.
I had my heart set on a Spencer rifle for a couple years and circumstances kept kicking me in the teeth so that I missed several. Then the collecting gods grinned in my direction and I ended up with an early Spencer rifle that I'm quite happy to have on display in the museum.
View attachment 536568