Half gallon of heavy whipping cream is 6500 calories, it is at Costco and I forgot the cost, if you are just going for calories and don't mind the non-paleo thing I only do it once in a while because of the non-paleo thing. Eating mainly 1-2 hours before bed keeps the weight on, and eating lots of carbohydrates before bed whether it is beer, fruit, or sweet potatos.
About the shakes, a post workout shake always made me hungry about 1-2 hours after I ate it. My shakes used to be 2 cups protein powder from TJ's, peanut butter, juice, frozen berries until almost solid.
Now if I do Post workoutt nutrition I eat a meal (1/2lb meat or fish; 1 starchy carb sweet potato, bananas, fruit; 1 small amount of fat, avocado or nuts