Those G-BUS* A320s were very early birds -100s if I'm not mistaken. The early aircraft had corrosion issues I believe so if they are looking at A320s they really need to be looking for cheap ones around the MSN 1000-2000 mark. The ones currently being built are in the 6000-7000 range.
They would also have to make a decision on which engines to go for too, as the CFM they have plenty of experience of is not great on the A321 should they decide to replace the 757s with them in the future. Unless they can get a deal from airbus on some traded in A320s I think they'd be better going for more 73NGs. As much as I prefer to fly on the Airbus over the Boeing and think it is a superior aircraft an most departments their experience on Boeing and the fact that they are already purchasing a fair few 738s means it would make much more sense to stick with the type.