Friends - our extremely non MMM friends, bought AN $800 real compressor type fridge and it worked great. An Australian model. Designed for camping.
I just bought the Coleman 5 extreme, 70 at for under $70. No one is selling them second hand and sales are rare. We used our last cooler for 20 yrs, so $70 is likely OK but seemed a lot for a cooler.
I too double zip lock all and freeze bottles of water, juice, ice pack, meat, almost everything in it is very cold or frozen atvyhe start. Everything is in plastic tubs ( yogurt containers) where possible. We use a second cooler for fresh foods and soggy items that would be bad are kept in a tray at the top only. (Bread) After 4 days, ( I am hoping for longer with the new cooler) we start to buy block ice. I either put it into its own tub, of wrap it three times in bags to seal it. Note that cold water getting all soggy is good insulator.
Tomorrow we are on a 10 day trip, and I will try to buy dry ice on day 5 instead of block ice.
Hubby bought an electronic cooler for the car snacks, so wed Weill see how long it lasts.