By all means buy it,it's worth that as a wall hanger and a little cash negotiating might even drop the price.Some good pictures including full length on both sides and close up of the butt and lock panels would help. Without seeing this gun I would guess that it would take at least $700.00 to $800.00 {more if you could find an old lock and guard}and a competent restorer,not necessarily a builder.For the time being LEAVE THE GUN ALONE until someone who knows what he is doing can be found.At the present time the market on guns like this is pretty soft and I would give serious consideration to using it as a wall hanger unless you can find repro parts which can be made to fit the mortices without damage to the integrity of the gun.
Without seeing the gun it is hard to identify the period and place of origin for guns like this one.At a local show recently another collector and I appraised a nice rifle, brass mounts with a little added brass trim and possibly a cap box ,but overall a very nice decorator. I put about $1000 to $1,200 and the other collector who makes more shows than me put $900.00 to $1200.I think it would sit on a table a long time before it brought any more.
Good luck
Tom Patton