It's a demijohn, probably French. I would note that the value is not nearly what is being asked for that on Chez Pluie...I've had a few identical to the one you have and struggled to get more than $60-$80 for them.
This is a very standard style of French demijohn and they are not nearly as old as they look. You can see some typical asking prices and sold prices on eBay if you are curious. As I noted before, if you have a $300 offer you should take it.