Wow, R24 to insulate a basement might be a bit extreme, but I suppose that far north it may be a necessity. I just completed a walk in fridge for my home for beer storage. In doing research for it I learned that commercial fridges are built to r30 and freezers typically to r35. Because of this they tend to be fairly efficient unless you have people in and out of them all day. In finishing the rest of the basement I'm using r19 as I figure I still want some natural cooling for the summer time so that I don't need to use AC on that level. The big thing with my fridge was that once I competed it I wrapped the entire thing with Reflectix, basically aluminum foil on both sides of bubble wrap. It's supposed to create a seal and take care of the studs leaking heat and it's a heck of a lot cheaper than $1 per foot, and it covers the entire wall. The only issue I had with it was putting drywall on top and getting it screwed down tightly.

I'm able to keep it at a cool 40 degF with my cooling unit kicking on for about 5-10 minutes every couple of hours. It's cheaper to cool my 6'x9' walkin than my much smaller kegerator.

-Luke.