Any particular reason it has to be Mullers? There are loads of other syn free yoghurts - see thread in the syn value section - and I know that activia single pots are on BOGOF in tesco and shape feel fuller are only £1 for 4 pots.
I just love mullers I guess, they make great icecream, especially the strawberry one, but the shape fuller are very nice to eat, I bought them when they were on offer once, they were scrummy.