Their latest charge is �28 for an extra bit of hand luggage - which includes a carrier bag of duty free.
So, if you pick up some duty-free in the airpor before leaving and can't fit it in your hand luggage, you will be charged extra for taking it onto the plane.
Something else to consider is that if you have hold luggage, you will be charged for putting that into the hold per piece, per journey. You'll also have to check in at the airport which will cost you extra per person, per journey.
Have a look at Air Malta - they can often be reasonable on prices