Welcome to Mexico! That deposit is the worst. Also don't be surprised when after all the currency conversions they do you don't get back the full $400. We lost about $80 on currency conversions per bike. Also best to avoid Acapulco if at all possible. It's one of the worst cities for corrupt cops and extorting bikers. Both myself, and all but 2 overlanders I met travelling were extorted in Acapulco, and nowhere else in Mexico.
If you can stretch it that far, the next really good place to pick up cheap motorcycle parts is in Medellin, Columbia. Great place to pick up tires and parts. Easy to find TKC 80's, Shink 705's or Sahara 3's for less than in the States.