So if i understand you correctly, you want to sort by a value that has to be calculated based on the currency?
You can do this, but not within a wordpress wp_query of sorts.
Instead you can do one of two things:
Method 1: The “do more now, have less hassle later”-way:
On saving the currency and price in your save_post action, you calculate the AED-price and save it in an extra meta field. When you need to sort by price, you sort by the AED-price. You will have to save all existing prices again into the new meta_field, but you can do this easily with a function that is called once and then never again.
Method 2: The “I don’t care about db efficiency, i don’t want hassle”-way:
You have to write your conversion-function into the sql-query. As i don’t know what exactly your conversion function does, i can only point you into the right direction.
You need to add a filter to posts_clauses. In this filter function, you can manipulate the complete sql query parts, so you have to be very careful and implement checks so that you only change the query that you want changed, and not let’s say the query for your main menu.
You can read about this filter here: post_clauses.
Happy Coding!