Hi coldfeet999. I have done all 3 ! By all three I mean, IKEA kitchen, standard offering from Panelling centre and expensive option from Richard Burbridge at PC.
IKEA kitchens are very good. No doubt you have looked at their catalogue,
IKEA Kitchen Catalogue.
There is very little to a kitchen. First of all you have the carcass which differs very little. You have mentioned the backing which of course can be mixed and matched ie buy IKEA carcasses and use thicker backs if you wish.
Doors in IKEA - you get what you pay for. The cheaper doors are not worth getting, similar to Panelling Centre. Prices increase as the better the quality of wood. Plinths and surrounds are where you can save money by using mdf/chipboard. Kitchen gets dearer if you use solid wood for these components.
You can always go cheap on carcasses, and plinths and surrounds with better quality doors and save your money for a wow factor with counter tops either wood, marble or granite which can be sourced locally. You can also save yourself money by only having a veneer granite surface over say normal countertop.
If you dont know what you are doing with measurements you could go wrong with IKEA, eg if you broke one of the carcasses or pieces of wood that needed replacing. If you are not going to fit yourself (I did the first one myself - not too bad !) and got a fitter for the others). Actually I got the name of one from Panelling Centre who was truly excellent in that he was able to do electrical and plumbing work too. He gave us the wow factor by having solid wooden doors and overpainting the cheaper materials which meant we could go for the marble counter top which was a worthwhile luxury. If you want his name and number I will dig it out for you when I am at home.
PS - IKEA have all the gadgets for the inserts for discounted prices too.