Free: Contests & Raffles.
$400 will get you an Eberlestock or a Badlands 4500 or something like that unless you go used. If you want to go with a backpacking/REI style pack and not a hunting specific pack, that would open up more options. Mystery Ranch, Kifaru and the like I don't think you'll touch for $400.00 unless you go used and a few years old with some miles on them.
i like my eberlestock blue widow
For $439 you can get a Mystery Ranch Longbow. It has enough room in the bag to carry 3-4 days worth of gear. Furthermore ( this is why I bought it). You can put meat between the bag and the frame, while at the same time carrying ALL your gear. I have used it as a day pack, and as a bivy hunting pack. I have boned out meat and carried it in the bag and I have also sandwhiched a quarter of elk between the bag and frame with gear in my bag. Both work well. Very comfortable and durable pack. The 3 zip design is awesome. If I have a rain jacket stuffed in the bottom of my bag I don't have to dump my bag to get to it like other packs. I unsold it down and pull out the jacket. This feature is priceless. It also has inside pockets which seperate and organize gear well. I LOVE them. Check it out. http://www.mysteryranch.com/hunting/nice-frame-packs/nice-longbow-packHere's a few pics of it in action Now if you want something with more bag space than 2,400 cubic inches than check out the brand new Metcalf. This will be my next bag. It costs $469 and seems to be a great pack. Same concept as the Longbow, just a bigger bag. The nice thing about the Mystery Ranch NICE frame is once you have it you can use the Longbow for a day pack/meat hunter and then you can take it off and put on the 6500 bag if your doing a 10day bivy hunt. http://blog.mysteryranch.com/2013/02/nice-metcalf/Here's some more propoganda a bunch of pictures of Mystery Ranch packs hauling meat and gear. http://onyourownadventures.com/hunttalk/showthread.php?t=245278