vehicles in zihua, best to purchase in Zihua or bring fom?

That would mean permanently importing your US or Canadian vehicle. There are only certain vehicles that are allowed to be perm imported, and there are costs involved. But the main thing is that Mexico has put a stop to all importations (for quite a few months now) while they overhaul the customs system and replace lots of officials, etc. My advice would be to check with aduana (customs) and get up to date info- of course as with most inquiries of substance almost everywhere, you will get different info from almost everyone you speak to. Perhaps you can find out if there is an accepted broker at the moment- all brokers were released with the stop in importations- perhaps they have reinstated some by now. To import, you must use a broker.
I hope I haven't confused the already confusing issue!