Good argument but there are a lot of flaws in your argument. Do you know that there price tags could have been different because not everyone can produce a particular product like rice? And as much as you and I and the rest here wanted to reduce hunger, this kind of setup will not help.
And I think every government is doing everything at their disposals to curb whatever issues they have in their own country. But we all know that there is no balance in power in this world and there are problems that inherent, hard to solved specially if it involves humanity, i.e world peace (now we have wars in the Middle East), hunger.
exactly,the price difference is there for a reason, its not because a government want to be different to each other its because the law of supply and demand at action.
whatever goods more common in your country than the other it will definitely have cheaper price since its more common that means the demand is having lower ratio to supply.
the world can't just set one price for all because the economy doesn't allow that, moreover we need also to delve into the difference of wages accross the world and how the currency strenght could affect the price of goods.
also, the cost of labor will definitely affect the price of goods in that country, for example, local shoes in south asian or southeast asian are definitely cheaper than local shoes in europe and so on.
doing the one price thing won't solve any problem instead it will make other problems appear.