Can users choose different currency for price of their ads?

The answer is Yes.

In component’s options, you can type what currencies will be available for users to choose while adding their ads.

Please note: this is just a currency sign, no currency conversions will be applied.

In back-end open Components -> DJ-Classifieds -> Options -> Prices tab -> Prices section 

and in  ->  Price unit list  type currencies seperated by semicolon ( ; ) and Save settings.

Now when a user submits the advert on the front, he'll be able to choose the currency.