Kevin, I suppose that by water closet you mean a high tank toilet. But this was not the only design available at the time. The modern placement of the tank just above the toilet was common by 1900.
$800 seems about right for a reproduction of a high tank (I paid about that much for mine). You might do better at at salvage yard, but how will you get parts to make the thing work? And I wouldn't even think of making one.
I would study some back issues of Old House Journal and get ahold of a Motts catalog to see what is historically appropriate and how you can achieve the result you want for the least cost.