the cheapest A-kasse which is open for everybody, is FTF A-kasse. You can find link on our site.
Only if you are a nurse, teacher og working in pedagogy you can find cheaper A-kasse.
I assume you do not work in one of these areas.
If so the best choice for you will be FTF A-kasse.
The cost is DKK 430/month. But you can deduct this in your tax, so the actually amount you pay is about half.