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Is it really like this? I'd have thought the latter would have meant that the prices are perhaps returning to a level from which they've fallen earlier...物価が下がっていく。
物価が下がってくる。
Both mean that prices continue to fall. Both tekuru and teiku indicate continuation in this example. However teiku implies motion away from, whereas tekuru implies motion towards.
You think prices are going away from you in sentence 1, such as when you don't like the trend. You think prices are approaching you in sentence 2, such as when you like it. (contributor: bi-ru)
Also, what is the difference between 値段 and 物価?