there are 2 Mexicos, the one next to the border and "interior or main land" Mexico, wait.. where are you?? I see you are from NZ I am thinking maybe you are somewhere north (USA) so maybe that can help some in sending stuff here.
AS I was saying the border area and Baja California (the peninsula) it is call a free area so duties are less and getting things from one point to the other is easier, if you are thinking of main land it will be expensive, that is all BUT another option is to buy it in Mexico. It will take time, unless you have a small bike (even this could take time).
Some more info could be nice to have, what bike do you have, where you want to ship stuff. and so on.
A motorcycle or scooter always turn a bad day into a great time!
KLR 650, Honda Beat scooter!!