As I recall, the DX series were MIK/MIC and relatively low quality, while the DKs are MIJ. Neither are generally regarded as "great", but the DX is considered by most to be, well, just shitty.
On the Ibanez side, a used 7620 is the de-facto standard for basswood, tremolo-ed sevens. You really can't go wrong with them, but they'll be a bit more than your price range. The 732x/742x aren't bad either for the price, which is around $300 new.