Typically a frequency dictionary tends to run about $35 to $45 dollars, US. The books Barron's puts out sort words by topics, (which is handy), but at some point you may want to just make sure you have cards for the top 1000 then 2000 then 3000 etc., most frequent words. 

I use the Routledge list for Japanese, since finishing the 625 list. The Wikipedia lists are fine, and they have a pretty attractive $0 price tag.

That said, the Routledge dictionaries have a few things that really do make them worth the extra money once your language has reached a level where you can really use them. They are theoretically more perfect in terms of which words are ranked where. That’s pretty irrelevant for us; we just want some good words to learn, and the top 1000 in Routledge or Wikipedia are both going to be high value words. 

The awesome thing about the Routledge list is it has really good, translated example sentences that show you exactly what the word means. You'll see how it’s used, and you can use those example sentences immediately in Anki to learn the words. It’s a *huge* time saver.  They’re also supplying information about parts of speech, gender, and proofread translation. In the Japanese list, they’re also grouping together alternate spellings for single words (which would end up with two different entries on a Wikipedia list). All these features, to me, are worth the extra money, because it ends up saving me at least a few hours of time in the long run, if not more.

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