Unless it is ridiculously cold (like not in Tassie) you won't wear a down jacket when walking, and at night there is always a sleeping bag. Like Geoskid said a waterproof jacket is more important, but man oh man aren't good ones of those expensive!
I have a Macpac Sundowner 600 loft down jacket and I am extremely happy with it and have never been close to cold wearing it around camp(down to about -3). Higher loft just means you can go lighter and less bulky for the same weight (but at more cost).
If you don't want to shop online I'd get a good value (i.e. cheaper)jacket (best I can see are the Macpac Sundowner or Aurora), like Cam said compare fill weights as well as loft. Then keep the savings for a better rain coat. But do get one with at least a very basic water repellent coating.
Unfortunately nobody seems to have down jackets REALLY on special at the moment. I paid $179 for mine last year and a mate paid $150 for his similar but different brand one.
Now on rain coats I don't know. I have a Kathmanpoo NGX. It was okay when new but now it wets out and doesn't breathe much, as will happen on even the most expensive Gore-Tex & Event ones if you don't renew the DWR coating. (whoops there I go using techy acronyms

) I got it for $180 so I don't regret buying it. Personally I think I'd either go for a cheap proprietary membrane like NGX, Repel, Toray etc. or go the whole hog and get Event jacket. My next coat will be Event. Of course a $50 coat will keep the rain off as well and if you don't tend to sweat much they are okay, albeit a bit more fragile. Not sure of your size but
THIS is a bargin!
I just read through the whole topic for the first time from top to bottom and oh boy it's like you ask a question and smacked in the face with an encyclopedia of answers! So sorry but thats my opinion to add to the encyclopedia! Good luck and happy shopping
