Hi appletiser , I am currently Dukaning and it is great, really really easy as it is so simple (but it isn;t for everyone). I gained quite a bit of weight over two pregnancies and so far have shifted nearly 20lbs since mid -Oct! There is a thread on this board for Dukaners here and a seperate recipe thread herehas just been set up to help.
I find it actually easier now to cook for DH and my two DCs (both under 3.5) as I menu plan more and cook a lot of casseroles, mince etc I just add rice, pasta, potatoes, cheese etc to their portions which seems to work really well.
Re cost for me I think I am not spending as much but that is because a) I am not buying alcohol and b) I think I am menu planning better so no food is wasted (ie if I roast a whole chicken it can feed us all for at least 2 maybe 3days as I will make the remains into soup etc), plus I don;t buy expensive cuts of meat or fish (ie I use a lot of lean mince, casserole beef, frozen fish fillets, chicken thighs and a lot of eggs.) Muller light yoghurts are my staple 'sweet thing' and they are always on offer somewhere.
oh you don;t need to register anywhere, getting hold of the book will be all you need but tbh you can glean a lot of info from the internet.
good luck! PS if Dukan isn;t right for you, then low-carbing is very similar and effective just a little less restrictive, I think and there is a great low-carb thread on this board.