Personal recommendation would be Petersons - however to clarify - NOT Petersons House (champagne house i think its called?) and there is a Petersons cellar on Broke road however i would very highly recommend going to the Mount View Petersons cellar, its only an extra 7~ or so min drive however the area and cellar are worth it.
As the other guys are mentioning, not really anything on "sale" but more just limited releases/or lack of supply to send out to bottle shops for a big release, so you'd be paying the cellar door prices. It's more about being able to taste bottles and find out if there is anything you like/enjoy and realising "oh wow this is mentally good. i need a few bottles of this." because:
1) the vineyard probably doesn't sell it at dan murphy's because they don't make the quantity to be able to support that level of volume
2) they don't need to sell beyond the cellar door, they have regulars/customer bases and membership groups that enjoy/buy up their wines due previous visits or long time buyers.
3) even if you're paying the "extreme" cellar door price of 50 or 60 dollars for a bottle, you may taste a wine that you think performs far above that price range and would be happy to pay the now "cheap" price of 50 or 60 dollars for it.
Value is definitely in the eye of the beholder here =)