What you are all referring to is the double roller blind that attaches to the back seat. It is a carge net and cover. The two attachements positions are for the carge net in the two positions of the backrest, upright or folded. Don't for one minute think of it as a dog guard (unless you have a very small dog!) its purpose is to prevent small objects coming forwarsd in a crash.
So far as I am aware it is a standard fitment on all estates (wagons), not an extra
$1250 is probably the right price new, I was quoted about £600 2 years ago. If your dealer wants to charge you for fitting, he's an arsehole, you fit and remove it yourself by simply sliding it onto the fittings in the left side backrest.
Take motard's advice, I paid £40 for mine.
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)