The link below is on historical gas prices. Also include a link on US dollar to Euro. Depending on the state we are currently at about 2.50 and have been over 3.50. The dollar menu going to 5 because of a 10% or 20% drop in currency doesn't seem likely. We, and also other countries, can have fairly big currency changes without much internal inflation or deflation(can depend on country size). A number of countries have actually deliberately devalued their currency in order to encourage growth. The question that is more interesting is can we lose high productively jobs(manufacturing...) and still keep high standards of living. The data indicates we cannot.
https://www.statista.com/statistics/204740/retail-price-of-g...
https://www.macrotrends.net/2548/euro-dollar-exchange-rate-h...