Prices in Mexico, or in any other Latin American country for that matter, are always inflated. I remember when I got my SNES over there (Mexico); it cost me like $1,000 pesos (the exchange rate in those days was $1US = $3MEX); at that time the system was about $150US.
To be honest, I don't think it's Sony itself that's responsible for this. Sales agencies over there are very corrupt and like to make big profits. I wouldn't be surprised if most of that extra cost is due to some BS tax or "handling" fee.