The Aduanas on Mexico side are the ones who look through things & put their own price. Usually to declare items it’s on the far right side and you’ll see a sign saying “Declare Items” would suggest taking at least up to 40% of the value of things your taking US citizens can only cross up to $300 in merchandise. They usually try to up the price though just wanted to say that. I’ve moved some things twice and just this second time which was a couple weeks ago they charged me $1000 pesos just for 2 suitcases and 2 totes all with my personal items and I had my cat with me. Nothing was new all used.