Shameless plug, but I happen to have a kifaru duplex light with 44 mag for sale in your budget.
A 50lb load is easy to carry with that frame. (Had 125lbs on a pack out once).
What you described would fit inside the 44 mag with no need to mess with the meat shelf. The bag zips completely open and is really easy to access and load/unload.
If you like the idea of using the shelf, I would recommend the stryker xl or hellbender. I don't like using the shelf on kifaru's other bags.