How can we get price reductions (from suppliers) based on Economic Conditions, Currency fluctuations etc (other than fuel)

In the past few years, Fuel and other factors contributed to price increases, and suppliers increased prices, but how do we incorporate price reductions, specially based on the economic conditions, eg. The currency exchange rate , political unrest ? how can we get the suppliers to incorporate reductions (other than getting quotes from their local currency) , ? what could be the disadvantages of getting quotes from local currencies in the current market conditions?