Why don’t you get some plexiglass and put a 6” pee and poop shield so the poop cannot slip our of the bars. That sounds like an awful lot of excrement for just 3 ferrets. Are you overfeeding by chance? Or if you are changing every day the box must be way too small for them. We had a 12 by 16 box for 4 guys and I scooped the litter once a day with no issues, my guys loved the clump litter, left no stinky left behind.
You can either use a small cat litter box or check on the different sized craft or sewing or storage boxes, they are plastic and come in just about every size and every color. Instead of complaining you should be looking at places like Kmart, target, Walmart etc, you won’t know until you measure what you think you will need. You can find these on line too in case your not able to get around.