What's the best way to plot a bar graph with large numeric difference in values?
A log scale will make the difference before and after revaluation look less extreme, and a log transformation is usually pretty defensible for things measured in units of currency (especially when there are no 0-value entries). Other transformations exist, but since this is mostly for aesthetics I don't think that you'd need much that a log transformation couldn't offer.

Fiddling with multiple vertical axes and continuity breaks may help, but at an almost-guaranteed cost of making the graph very difficult to view and interpret correctly. If you need to show both periods, I would probably log transform.

You will know your needs far better than I do, but I do question a little bit how valuable seeing the before and after this way is. The revaluation was an arbitrary decision introduced at an arbitrary time, and behavior of the currency before the revaluation is probably not very informative of anything that happened afterwards (and vice-versa). It's far from clear to me that there is much value in showing both at once like this, at least from my naïve look at a single graph.

The main reason I can think of to show both at once this way is to display how extreme the inflation was, in which case the scale differences would be a feature and not a bug.