When we left London in 1998 and moved to Skye, we took seven cats with us, including two totally new kittens. We put them all in a Guinea-pig hutch, two-storeys, jammed underneath a big chair for stability at the back of a huge Luton box van, with the bottom inch or two of the roll-up door open for fresh air and water bowl in the corner of the hutch. Two Guinea-pigs were evicted to a cat-box temporarily. The journey with various stops was about 22 hours. Some cats took to the upper storey some to the lower and the new kittens happily spat at the rest while soon having to get to know all the others. We still have one of the seven with us: Orange, one of the then new kittens, will soon be eighteen years old. As I write this, he is half asleep, but absolutely purring his head off, soo loud, trying to sit on Janet's head while she sleeps.
When we got to our new house, the cats descended from the van, went sauntering off around the outside of the house, doing a complex perimeter inspection, and then all went inside. New home adopted.
So our migration cost nothing really, as we had to have the van, full of furniture, anyway.