Holland and Barrett do a 'muesli base' which doesnt have raisins in, you just add what you want to it. It's got no sugar added either. I usually add almonds or hazelnuts but I'm not a fan of raisins or sultanas.
I don't know what they charge for this but it has to be a rip-off - you'd do much better to make it yourself from scratch. Muesli is hardly difficult to make.