I use a similar system as SD. I don't bring fresh food like steaks or frozen items, but I do bring cheeses and meat sticks that I want too keep cool.
I have a Granite Gear food pack, about $90. I got in on sale for about $50. I cut a piece of 1" close cell foam that fits the bottom of pack.
I use the same Sterilite boxes, except for solo, I use 2 of them.
To make it a "insulated" box, I wrap a 1/2" Thermarest foam pad around the boxes. Either the 20" or 25" will do, depending on how hight the boxes stack? I then have a piece of close cell foam as a " lid".
With this set-up, SD's freezer pack tips, I think you could get the same performance for a lot cheaper than $400.
Foam and pad serve a dual purpose. The foam wrap, protects the boxes from rocks and wear and tear as you portage.They also "quiet" the food pack. The Thermarest pad will make a great seat on wet or cold ground. You can even put it under your sleeping pad for a little extra comfort if you are forced to use a less than ideal tent area. Last, but maybe not least, if you dump, your heavy food pack will float, no problem

You can buy the Thermarest pad, Sterilite boxes, and freezer bags for under $50, and the close cell foam you can often find in commercial packing boxes. You could buy the food pack, and save $150 on the extras too make it an insulated pack.