First off, I was a bit confused by your post, it it a rifle with a cut stock or a rifle that has been cut down into a carbine? To me, a rifle that has a cut stock would not be worth more than $250 and that is only if it has a pristine bore. If it was cut down into a carbine the value goes down a bit more.
That gun sounds like it is not in very good condition and I would pass on it unless the price comes down.
I was shooting my 1884 Trapdoor rifle at the range the other day. A fellow approached me and offered a 1873 rifle in excellent condition (his description) with bayonet for $600.
I bought this 1884 a few months ago for $550: